seismic evidence for variations in axial magma chamber properties along the southern juan de fuca ridge abstract multichannel seismic data collected along the cleft segment on the southern juan de fuca ridge show that this intermediate spreading center is underlain by a mid crustal reflector interpreted as the top of an axial magma chamber amc the amc reflection is present along most of the segment and deepens gently from 2 0 km near the southern end of the segment beneath the ridge cleft observatory site to 2 3 km at the northern end beneath the site of the mid 1980s submarine eruption we analyzed the one dimensional seismic structure of the amc at two locations with contrasting lava chemistry beneath two different hydrothermal vent fields at the northern site waveform modeling in the time intercept slowness p domain indicates that the amc is 100 m thick and it is characterized by a decrease in p wave velocity from 6 km s to 3 7 km s in contrast the p wave velocity within the shallower 100 m thick amc at the southern site is higher 5 0 km s the decrease in seismic velocity within the amc indicates that it is partially molten and that it is not a cracking front as previously suggested for other intermediate spreading segments the data show a coherent seismic phase interpreted as the p to s wave conversion at the amc pamcs stacking of this event shows that the pamcs is only present along the northern part of the segment our results thus suggest along axis variations in the crystallinity of the amc the amc along cleft varies from a high crystal content

paleohydrology of buckskin mountain national district humboldt county nevada precious metal veins of the national district humboldt county nevada occur in strongly altered miocene volcanic rocks hydrothermal assemblages in buckskin mountain display a marked zonation from the paleosurface downward that correlates with the elevation and physical properties of enclosing rhyolites light stable isotope analyses indicate that meteoric water from two distinct sources comprised the ore fluid the delta d values in fluid inclusions from deep level quartz vein segments 1 250 ft 379 m below the palcosurface range from 115 to 129 per mil fluid inclusion waters from near surface quartz vein segments 0 to 1 250 ft 0 379 m below the paleosurface have delta d 86 to 125 per mil and are generally more depleted than local miocene ground water whose delta d is calculated at 85 per mil the delta d range in inclusion waters from near surface quartz veins has resulted from mixing of the fluids present in deep quartz veins with local ground water and condensed steam derived from boiling of both fluids the fluids present in deep quartz veins probably originated as precipitation on distal highlands with elevations approaching 6 000 ft 1 818 m oxygen isotope data from vein and wall rock minerals record increasing depletion as veins are approached indicating that quartz veins were the major conduits of fluid flow the degree of oxygen exchange between hydrothermal fluid and wall rocks water rock mass ratios and the abundance of hydrothermal phases increase toward the paleosurface the progressive influx of local ground water with increasing elevation is also indicated by chloride dilution the estimated duration of the buckskin mountain hydrothermal system 50 000 to 200 000 yrs is limited by the volume of high temperature alteration assemblages and the heat budget of a proposed intrusion thermal constraints and isotopic data provide an internally consistent range in lifetimes which is several times shorter than that proposed for some active hydrothermal systems these long lived modern systems apparently require multiple thermal and or intrusive events based on geologic isotopic and floral data the palcogeography of ancestral buckskin mountain was dominated by forested volcanic terrane having considerable relief an intermontane basin remnants of which comprise the summit of buckskin mountain today contained scattered thermal pools and patches of steaming ground the basin covered several square miles and stood at 3 000 ft above sea level while adjacent uplands were several thousand feet higher in elevation floras included subalpine spruce and fir mixed conifer hardwood slope forests and basin floor hydrophytes willow and marsh grasses buckskin mountain during the miocene closely resembled present landforms in yellowstone national park wyoming

late cenozoic evolution of epithermal gold metallogenic provinces in kyushu japan kyushu island japan is located at the junction of the southwest japan arc and the ryukyu arc there are two major late cenozoic epithermal gold silver provinces in kyushu which are termed the northern and southern provinces the provinces are characterized by 1 pliocene volcanism dominated by calc alkaline andesite followed by quaternary volcanism including extrusion of both calc alkaline and tholeiitic magmas 2 formation of extensional grabens 3 pliocene to pleistocene mineralization which was dominated by abundant low sulfidation ls epithermal deposits with a few high sulfidation hs examples the two epithermal gold silver provinces have evolved differently since about 5 ma the northern province has exhibited diminished hydrothermal activity from the pliocene to pleistocene whereas the southern province has witnessed increased hydrothermal activity mainly in easterly and northerly directions changes of tectonic setting from the pliocene to pleistocene account for the variable trends in epithermal gold deposit formation westward oblique subduction of the philippine sea plate beneath the southwest japan arc caused development of the hohi graben and arc related volcanism at about 6 ma this was associated with widespread ls mineralization in and surrounding the hohi graben as is represented by the bajo and taio deposits the subduction of the relatively buoyant kyushu palau ridge during the early pliocene strengthened the coupling between the slab and overriding ryukyu arc leading to polygenetic andesite volcanism with associated hs kasuga iwato and akeshi and ls kushikino mineral deposits forming in the southern province a change of the subduction direction of the philippine sea plate from west to north northwest in the early pliocene increased the orthogonal convergence rate between the southwest japan arc and the philippine sea plate resulting in a decrease of volcanic and hydrothermal activity in the hohi graben of the northern province the more northerly subduction of the philippine sea plate shifted the locus of the kyushu palau ridge subduction northward resulting in underplating of the older 85 60 ma negatively buoyant amami basin oceanic slab in the southern province rather than continued subduction of the young 27 15 ma buoyant shikoku basin slab this replacement caused steepening of the slab angle and slab rollback in the southern province which was associated with regional extension an eastward shift of the ryukyu volcanic front and development of the kagoshima and shimabara grabens as well as the okinawa trough rhyolite and basalt volcanism in addition to andesite volcanism have occurred since 2 ma in the area of the ryukyu back arc coincident ls mineralization at hishikari and ohkuchi was affiliated with the rhyolite volcanism another change of the subduction direction of the philippine sea plate to the northwest occurred at 2 1 ma the forearc sliver of the southwest japan arc shifted westward in association with right lateral strike slip faulting along the median tectonic line due to the increase of the westward convergence rate this shift resulted in shortening and cessation of graben development in the hohi area restricting the subsequent volcanism and related hydrothermal activity to the central part of the graben

the first measurements of hydrothermal heat output at 9 50 n east pacific rise abstract despite the importance of the heat output of seafloor hydrothermal systems for the earth s energy budget hydrothermal heat output measurements have been very limited in this paper we report the first measurements of hydrothermal heat output at the ridge 2000 integrated study site on the east pacific rise we focused our work on the bio 9 complex situated at 9 50 n where there has been an extensive measurement and sampling program since 1991 this site is located along the eruptive fissure of the 1991 1992 event and the site of the 1995 earthquake swarm we made direct measurements of advective heat output at several individual vents and at one site of diffuse flow tica although these data do not describe the complete heat flux picture at this vent field the data yield a total hydrothermal heat output of 325 160 mw with 42 21 mw coming from high temperature vents along this 2 km segment of ridge this result assumes a diffuse flux similar to that measured at tica occurs at each high temperature vent site our initial measurements thus suggest that the heat output of the low temperature diffuse venting is approximately 10 times that of the high temperature vents but may also be one or two orders of magnitude greater

sub bottom temperature anomalies detected by long term temperature monitoring at the tag hydrothermal mound during aug 1994 feb 1995 geothermal measurements were carried out on the tag hydrothermal mound 26 0 n 44 49 w of mid atlantic ridge two geothermal probes made reliable measurements six transient anomalies in subbottom temperatures were detected 20 m south of the central black smoker complex cbc having durations 40 to 400 hours and magnitude 0 2 c to 30 c these anomalies are probably evidence for short period fluctuations in the fluid circulation beneath the mound the time variability in subbottom temperatures near cbc suggests that instantaneous heat flow measurements may not represent the time average of heat flow there although it is difficult to specify the origin of thermal anomalies during the drilling period by the ocean drilling program at least one of them seems to correlate with the drilling events because it was also accompanied by transient temperature anomalies at cbc and 50 m east of cbc observed by other instruments

tidal current effects on temperature in diffuse hydrothermal flow guaymas basin a twelve day record of temperature collected from the diffuse flow area of a guaymas basin hydrothermal site exhibits variations from a minimum of 3 05 c to a maximum of 4 87 c whose periodicity is correlated with tides measured at the nearby town of guaymas a simple model based on the hypothesis that temperature variations result as changes in tidal bottom currents induce changes in the height of the thermal boundary layer is in good quantitative agreement with observed temperatures for most of the record the success of this model illustrates that the effects of tidal currents can be strong enough to dominate the time variability of a temperature signal at a fixed point in hydrothermal flow therefore tidal currents must be taken into account when using temperature measurements to estimate time varying heat fluxes from hydrothermal diffuse flow regions

measuring fluid flow and heat output in seafloor hydrothermal environments we have designed built calibrated and tested new anemometer and turbine flow meter devices to measure fluid velocity at high and low temperature focused and diffuse discharge sites at oceanic spreading centers the devices perform at ocean floor depths and black smoker temperatures and can be used to measure flow rates ranging over two orders of magnitude flow velocity is determined from the rotation rate of the rotor blades or paddle assembly these devices have an open bearing design that eliminates clogging by particles or chemical precipitates as the fluid passes by the rotors the devices are compact and lightweight enough for deployment from either an occupied or remotely operated submersible the measured flow rates can be used in conjunction with vent temperature or geochemical measurements to obtain heat outputs or geochemical fluxes from both vent chimneys and diffuse flow regions the devices have been tested on 30 alvin dives on the juan de fuca ridge and 3 jason dives on the east pacific rise epr we report 102 new measurements over a wide range of discharge temperatures 5 363 c velocities 2 199 cm s and depths 1517 2511 m these include the first advective heat output measurements at the high rise vent field and the first direct fluid flow measurement at middle valley our data suggest that black smoker heat output at the main endeavor vent field may have declined since 1994 and that after the 2005 2006 eruption the high temperature advective flow at the epr 9 50 n field may have become more channelized predominately discharging through the bio 9 structure we also report first direct advective measurements in the lau basin and at the epr 9 39 5 n with flow meters that predated devices described in this work and were used in the process of their development we discuss potential error sources and how they may affect the accuracy of measurements by our and other devices in particular we use the turbulent plume theory to evaluate the effect of entrainment of ambient seawater

1 2 epithermal pb zn cu au deposits in the baia mare district eastern carpathians romania baia mare district lat 47 40 n long 23 34 e 1 2 epithermal pb zn cu au deposits in the baia mare district eastern carpathians romania baia mare district lat 47 40 n long 23 34 e k kouzmanov l bailly c t mas p iv scanu a isotope geology and mineral resources eth sonneggstrasse 5 8092 zurich switzerland b brgm rem mesy 3 av claude guillemin bp 6009 45060 orleans france c dept of mineralogy babes bolyai university 400084 cluj napoca romania d geological institute of romania caransebes str 1 78344 bucharest romania received 19 november 2004 accepted 1 may 2005

tide related variability of tag hydrothermal activity observed by deep sea monitoring system and obsh abstract hydrothermal activities were monitored by an ocean bottom seismometer with hydrophone obsh and a composite measuring system manatee including ctd current meter transmission meter and cameras at a small depression on the tag hydrothermal mound in the mid atlantic ridge low frequency pressure pulses detected by the hydrophone with semi diurnal periodicity seem to correspond to cycles of hydrothermal upflow from a small and short lived smoker vent close to the observing site the peaks of pressure pulses are synchronous with the maximum gradient of areal strain decrease due to tidal load release microearthquakes with very near epicenters occur sporadically and do not appear to be directly correlatable to hydrothermal venting temporal variations in bottom water temperature also have semi diurnal periodicity but are more complicated than the pressure events temperatures may be affected both by upwelling of hot water and by lateral flow of the bottom current changing its directions with ocean tide

tracking meteoric infiltration into a magmatic hydrothermal system a cathodoluminescence oxygen isotope and trace element study of quartz from mt leyshon australia the oxygen isotope and trace element composition of hydrothermal quartz has been integrated with scanning electron microscope cathodoluminescence sem cl images and fluid inclusion properties to track fluid sources and hydrothermal processes in the mt leyshon an deposit australia oxygen isotope and trace element data were collected on parallel traverses across the same quartz sections using secondary isotope mass spectrometry sims and laser ablation inductively coupled plasma mass spectrometry la icp ms respectively with sem cl images obtained before analysis for petrographic context over the 280 to 650 degrees c quartz precipitation range suggested by fluid inclusion microthermometry delta o 18 quartz varies from 0 0 to 14 4 o corresponding to a wide range of equilibrium delta o 18 fluid values from 6 1 to 10 2 o vs v smow the delta o 18 quartz signature varies systematically among distinct sem cl quartz generations both within and between samples and can be correlated with variations in temperature and fluid composition but is independent of intra generational oscillatory zoning in contrast al and li concentrations correlate broadly with cl intensity in oscillatory quartz whereas their concentration is unpredictable in sealed fractures and overgrowths concentrations of b mg na p cl k ti mn fe ge and sn are independent of al li and oscillatory cl features but ti correlates with quartz precipitation temperature although no systematic correlation between delta o 18 quartz and trace element concentrations was found complementary patterns exist in narrow overgrowths of low delta o 18 quartz similar to 0 o and high al g 10 000 ppma these quartz zones likely formed during the incursion of o 18 depleted meteoric water into the magmatically dominated mt leyshon hydrothermal system we interpret the highest al concentrations as the result of high quartz precipitation rates triggered by depressurisation of the hydrothermal cell the decoupling of oxygen isotope and trace element patterns in quartz leads to the suggestion that 1 under most circumstances temperature and fluid chemistry dominate delta o 18 quartz and 2 the trace element record and in particular al and li is influenced by the superimposed effects of quartz precipitation rate c 2007 elsevier b v all rights reserved

effects of serpentinization on the lithospheric strength and the style of normal faulting at slow spreading ridges rock deformation experiments indicate that serpentinization can strongly influence the strength and tectonics of the oceanic lithosphere strength versus depth profiles calculated for conditions appropriate for slow spreading ridges indicate that the presence of serpentinite can reduce the integrated strength of the lithosphere by up to 30 results from flexural fault models indicate that if serpentinization is isolated to fault zones strain localization should be enhanced providing an explanation for the variations in the style of normal faulting along slow spreading ridge segments at segment centers where serpentinites are scarce deformation is accommodated on closely spaced faults with small throws at the segment ends where serpentinites are most abundant faults are widely spaced and have large throws q 1997 elsevier science b v

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

porphyry epithermal transition maricunga belt northern chile the refugio aldebaran and la pepa districts in the maricunga belt of northern chile contain advanced argillic alteration zones that locally host high sulfidation epithermal gold deposits in proximity to porphyry gold copper deposits the spatial association suggests a genetic link mineralized zones are characterized by four main vein types that formed at different times and have specific zonal relationships a veinlets are the earliest and deepest vein type they are restricted to potassic alteration zones in intrusive rocks a veinlets contain variable amounts of quartz magnetite biotite and chalcopyrite and locally have k feldspar halos they have nonmatching irregular vein walls and lack internal symmetry hypersaline liquid rich inclusions coexisting with vapor rich inclusions in a veinlets indicate temperatures as high as nearly 700 c and pressures between 200 and 400 bars assuming a lithostatic load depths of 0 8 to 1 6 km are inferred zones of abundant a veinlets contain mostly 1 ppm gold and 0 1 to 0 4 percent hypogene copper banded quartz veinlets occur mostly above a veinlets and cut a veinlets where they overlap dark gray bands the color resulting from a high density of vapor rich fluid inclusions and micron sized grains of magnetite commonly occur as symmetric pairs near the vein walls vein walls are parallel and slightly wavy vuggy vein centers are common and alteration envelopes are absent data from rare liquid rich inclusions in banded quartz veinlets indicate temperatures 350 c at pressures between 20 and 150 bars assuming a hydrostatic load depths of 0 2 to 1 5 km are inferred zones of abundant banded quartz veinlets generally contain 0 5 to 2 ppm gold and 0 1 percent hypogene copper d veins are pyrite veins with quartz sericite pyrite halos they are widespread and crosscut a veinlets and banded quartz veinlets the brittle nature of d veins and limited fluid inclusion data suggest temperatures 400 c d veins serve as important time lines they are nowhere truncated or crosscut by intrusions a veinlets or banded quartz veinlets quartz alunite replacement veins referred to as ledges in this paper are typical of the high sulfidation epithermal environment they are mostly limited to overlying volcanic rocks they contain local core zones of vuggy residual quartz that can contain enargite or at higher elevations barite of the three districts studied only la pepa has mineable quartz alunite ledges which contain an average gold grade of about 20 ppm a spectrum of porphyry style deposits exists cerro casale at aldebaran shares many characteristics of porphyry copper deposits worldwide whereas verde at refugio is a true porphyry gold deposit potassic alteration zones and a veinlets are strongly developed at cerro casale whereas they are absent at verde banded quartz veinlets predominate at verde whereas they occur only at the upper levels of cerro casale the pancho deposit at refugio and the cavancha deposit at la pepa are telescoped systems in which banded quartz veinlets overprint potassic alteration zones and a veinlets a veinlets and banded quartz veinlets cut and are cut by intrusions indicating multiple cycles of intrusion potassic alteration a veinlets banded quartz veinlets during formation of porphyry style mineralization banded quartz veinlets are thought to have formed by flashing of magmatic fluids during episodic transitions from lithostatic to hydrostatic pressure loss of sulfur to the vapor phase during flashing inhibited formation of copper sulfides in banded quartz veinlets and therefore resulted in high gold copper ratios where rising magmatic vapors condensed into overlying meteoric water along faults barren quartz alunite ledges formed this conclusion is supported by equivalent 40ar 39ar dates on hydrothermal biotite associated with porphyry style ore and alunite from barren ledges at aldebaran 40ar 39ar dates at la pepa indicate alunite formed at least 140 000 years to as long as 900 000 years after hydrothermal biotite within the high sulfidation epithermal environment the development of ore depends on the ability of late moderate salinity magmatic fluids to reach the surface without condensing a brine upon ascent cooling and boiling of the moderate salinity fluid below its critical temperature results in the formation of sericite at depth and alunite near the surface that is essentially synchronous with high sulfidation ore formation the timing of the switch from lithostatic pressures to brittle hydrostatic conditions relative to the life of the hydrothermal system might determine how much porphyry style ore forms relative to high sulfidation epithermal ore

earth s copper resources estimated from tectonic diffusion of porphyry copper deposits improved estimates of global mineral endowments are relevant to issues ranging from strategic planning to global geochemical cycling we have used a time space model for the tectonic migration of porphyry copper deposits vertically through the crust to calculate earth s endowment of copper in mineral deposits the model relies only on knowledge of numbers and ages of porphyry copper deposits earth s most widespread and important source of copper in order to estimate numbers of eroded and preserved deposits in the crust model results indicate that 125 895 porphyry copper deposits were formed during phanerozoic time that only 47 789 of these remain at various crustal depths and that these contain 1 7 1011 tonnes t of copper assuming that other types of copper deposits behave similarly in the crust and have abundances proportional to their current global production yields an estimate of 3 1011 t for total global copper resources at all levels in earth s crust thus 0 25 of the copper in the crust has been concentrated into deposits through phanerozoic time and about two thirds of this has been recycled by uplift and erosion the amount of copper in deposits above 3 3 km a likely limit of future mining could supply current world mine production for 5500 yr thus quantifying the highly unusual and nonrenewable nature of mineral deposits

fine scale seismic structure of the shallow volcanic crust on the east pacific rise at 9 50 n upper crust in a 3 3 km field area centered on the east pacific rise at 9 50 0 n we detonated 18 explosive shots 18 sources in a circular pattern 1 5 km radius on the rise axis and recorded seismic arrivals with eight ocean bottom seismometers eight receivers we observed 30 40 hz compressional body waves from all shots 144 p waves and 1 3 hz stoneley interface waves on a subset of source receiver pairs 58 interface waves using a station correction inversion we find that roughly half of the variance in the p wave first arrival times results from lateral variations in the thickness of the surface low velocity layer slvl a layer of extremely porous lava and basalt breccia with an average p wave velocity of 2 2 km s 1 the slvl thickness increases from 20 m along the axial summit trough ast to 120 m at near axis lava depocenters which are not symmetric about the rise axis depocenters are located 0 5 km to the west and 1 5 km to the east of the rise axis tomographic inversion of the stoneley wave first arrivals reveals that shear velocities in the slvl covary with the layer thickness exhibiting a similar asymmetric pattern with shear velocities increasing from 320 m s 1 near the ast to 520 m s 1 at the near axis depocenters our analysis demonstrates that the seismic characteristics of the extrusive layer near the rise axis are related primarily to volcanic features and processes the thickness and velocity of the slvl are low on the axis and within channel networks that deliver lava flows away from the axis and then increase rapidly at the distal ends of the channels where the lavas are deposited we find that azimuthal anisotropy exerts only a weak influence on our p wave first arrival times which we model as weak 4 seismic azimuthal anisotropy in the upper dikes with a fast axis oriented n23 32 w we find no evidence for seismic azimuthal anisotropy in the extrusive layer index terms 3025 marine geology and geophysics marine seismics 0935 3035 marine geology and geophysics midocean ridge processes 7220 seismology oceanic crust

the role of exhumation in the temporal distribution of ore deposits we show here that the temporal age frequency distribution of ore deposits is controlled largely by exhumation the combination of burial uplift and erosion that exposes subsurface rocks and ore deposits exhumation rates calculated from modal ages and emplacement depths for epithermal porphyry copper and orogenic gold deposits of phanerozoic age are 167 158 and 63 m m y respectively these rates agree with rates estimated for continent scale terranes by numerous independent methods thus the scarcity of precambrian epithermal and porphyry copper deposits is probably due to their removal by exhumation archean and pale oproterozoic orogenic gold deposits are more abundant than indicated by the exhumation record of their phanerozoic counterparts suggesting that the precambrian deposits formed in greater numbers recognition of the pivotal role of exhumation requires that the temporal distribution of ore deposits be corrected for this effect before it can be used as an indicator of large scale changes in earth history

constrained circulation at endeavour ridge facilitates colonization by vent larvae understanding how larvae from extant hydrothermal vent fields colonize neighbouring regions of the mid ocean ridge system remains a major challenge in oceanic research1 2 among the factors considered important in the recruitment of deep sea larvae are metabolic lifespan the connectivity of the seafloor topography and the characteristics of the currents3 here we use current velocity measurements from endeavour ridge to examine the role of topographically constrained circulation on larval transport along ridge we show that the dominant tidal and wind generated currents in the region are strongly attenuated within the rift valley that splits the ridge crest and that hydrothermal plumes rising from vent fields in the valley drive a steady near bottom inflow within the valley extrapolation of these findings suggests that the suppression of oscillatory currents within rift valleys of mid ocean ridges shields larvae from cross axis dispersal into the inhospitable deep ocean this effect augmented by plume driven circulation within rift valleys having active hydrothermal venting helps retain larvae near their source larvae are then exported preferentially down ridge during regional flow events that intermittently over ride the currents within the valley

characteristics of magma driven hydrothermal systems at oceanic spreading centers 1 we use one and two limb single pass models to de termine vent field characteristics such as mass flow rate q bulk permeability in the discharge zone kd thickness of the conductive boundary layer at the base of the system magma replenishment rate and residence time in the discharge zone data on vent temperature vent field area heat output and the surface area and depth of the subaxial magma chamber amc constrain the models the results give q 100 kg s kd 10 13 m2 and 10 m essentially independent of spreading rate and detailed characteristics of the amc in addition we find no correlation between heat output at individual vent fields and spreading rate or depth to the amc we conclude that high temperature hydrothermal systems are driven by local magma supply rates in excess of that needed for steady state crustal production and that crustal permeability enables hydrothermal circulation to tap magmatic heat regardless of amc depth using data on partitioning of heat flow between focused and diffuse flow we find that 80 90 of the hydrothermal heat output is derived from high temperature fluid even though much of the heat output discharges as low temperature fluid in some cases diffuse flow fluids may exhibit considerable conductive cooling or heating by assuming conservative mixing of diffuse flow fluids at east pacific rise 9 50 n we find that most transport of metals such as fe and mn occurs in diffuse flow and that co2 h2 and ch4 are taken up by microbial activity

tectonism and exhumation in convergent margin orogens insights from ore deposits abstract three widespread and abundant types of ore deposits epithermal silver gold ag au porphyry copper cu and orogenic gold au form by hydrothermal activity during tectonic convergence along continental margins and their preservation provides new insights into rates of those processes that form and destroy ore deposits as well as overlying rock ages for each of the three deposit types define lognormal age frequency distributions that are nearly identical in form but differ in their modal ages epithermal ag au porphyry cu and orogenic au deposits exhibit age modes at 3 11 and 199 ma respectively these ore types form at depths of 0 5 1 9 and 10 km respectively such that modal age increases with depth of ore emplacement qualitatively the dearth of deposits younger than their modal age reflects the fact that ore deposits form at depth within the crust and time is required for exhumation to expose them continued erosion serves to destroy ore bodies giving rise to fewer deposits

some metallogenic features of gold and copper deposits related to alkaline rocks and consequences for exploration porphyry copper gold skarn copper gold sediment hosted carlin style gold breccia pipe low sulphidation epithermal gold pluton related mesothermal or orogenic gold vein and volcanogenic massive sulphide deposits associated with alkaline rocks are commonly broadly similar to those hosted by their calc alkaline counterparts in contrast porphyry molybdenum gold deposits are confined to alkaline igneous centres alkaline suites are notably deficient in high sulphidation epithermal gold deposits and even in the advanced argillic lithocaps which host them this is surprising given that the required oxidised sulphur species are seemingly more abundant than in calc alkaline igneous centres highly efficient buffering of acidic fluid by metasomatised alkaline rocks may offer a viable explanation all types of intrusion related zinc deposits also appear to be poorly developed in alkaline provinces the characteristics of several gold and copper deposits associated with alkaline rocks including the giant porgera cripple creek ladolam olympic dam and phalaborwa examples are judged to diverge appreciably from their most closely related deposit types rendering them arguably unique most of these aberrant mineralisation styles may be due to variations in magmatic fluid compositional and liberation characteristics consequent upon the extreme diversity of ore related alkaline magmas most types of gold and copper deposits developed in calc alkaline provinces also constitute exploration targets in and around alkaline igneous centres although porphyry copper gold and low sulphidation epithermal gold deposits are considered to possess the greatest potential perhaps of even greater interest however is the possibility of encountering unconventional giant gold and copper deposits which lack closely analogous examples if already defined aberrant deposits are truly unique then exploration designed specifically to detect additional examples is pointless furthermore exploration for new unique deposits is difficult because their defining geological parameters are unknown alkaline rocks within or behind calc alkaline arcs at convergent plate boundaries probably offer the greatest exploration potential although anorogenic intracontinental extensional settings should not be ignored

epithermal au ag and related deposits of the hauraki goldfield coromandel volcanic zone new zealand epithermal au ag vein deposits of the hauraki goldfield in the coromandel volcanic zone new zealand produced 320 000 kg au and 1 5 million kg ag between 1862 and 2006 from a total land area of approximately 2 900 km2 approximately 69 percent of the production was from the world class martha deposit at waihi some 97 percent of total past gold production was from deposits hosted in miocene andesite and dacite of the coromandel group although this unit represents only 61 percent of the rocks exposed in the goldfield the deposits consist of quartz calcite vein systems 0 5 to 4 5 km long within alteration zones up to 20 km2 in size they were mined over vertical intervals of 170 to 330 m but up to 575 m at martha and 700 m at karangahake electrum and acanthite are the main ore minerals although pyrite sphalerite galena chalcopyrite sulfosalt minerals and te and se bearing minerals are present in some deposits stibnite and cinnabar occur locally as late minerals and some deposits are overprinted by late massive calcite fluid inclusion ice melting temperature tm measurements indicate that fluids associated with base metal and precious metal deposition had apparent salinities of between 0 5 and 2 wt percent nacl equiv with a maximum of 6 1 wt percent nacl equiv when fitted to hydrostatic boiling point with depth curves the homogenization temperature th data define paleodepths spanning a vertical interval from near the water table to a depth of approximately 1 300 m the presence of vapor rich fluid inclusions and occurrences of lattice textures and vein adularia indicate that periods of boiling coincided with deposition of some epithermal ores sulfur and carbon isotope values of vein minerals are consistent with a magmatic origin for sulfur and carbon oxygen isotope values of vein quartz and calcite are consistent with derivation from evolved meteoric water with possibly a small magmatic water component in some samples the epithermal deposits can be broadly subdivided into northern southern and eastern groups based on their host rocks age variability of vein strike au ag ratios occurrence or relative abundance of key minerals such as adularia calcite and arsenopyrite the grain size of vein quartz and differences in vein textures early ca 14 10 ma steeply dipping planar veins occur in the oldest andesite and dacite in the northern portion of the goldfield but some of these are bonanza grade veins that contained significant gold resources larger veins typically with well developed crustiform textures formed in andesite and dacite in the southern gold field at 7 to 6 ma and these contributed most of the au and ag that has been recovered from the goldfield in contrast rhyolite in the eastern goldfield hosts smaller less well developed veins plus stockworks that have produced the least amount of au and ag epithermal mineral deposits in the hauraki goldfield evolved through time reflecting changes in volcanic activity and more speculatively tectonic and structural history and setting

temperature variations at diffuse and focused flow hydrothermal vent sites along the northern east pacific rise in the decade following documented volcanic activity on the east pacific rise near 9 50 n we monitored hydrothermal vent fluid temperature variations in conjunction with approximately yearly vent fluid sampling to better understand the processes and physical conditions that govern the evolution of seafloor hydrothermal systems the temperature of both diffuse flow low temperature and focused flow high temperature vent fluids decreased significantly within several years of eruptions in 1991 and 1992 after mid 1994 focused flow vents generally exhibited periods of relatively stable slowly varying temperatures with occasional high and low temperature excursions lasting days to weeks one such positive temperature excursion was associated with a crustal cracking event another with both positive and negative excursions demonstrated a subsurface connection between adjacent focused flow and diffuse flow vents diffuse flow vents exhibit much greater temperature variability than adjacent higher temperature vents on timescales of a week or less temperatures at a given position within a diffuse flow field often varied by 5 10 c synchronous with near bottom currents dominated by tidal and inertial forcing on timescales of a week and longer diffuse flow temperatures varied slowly and incoherently among different vent fields at diffuse flow vent sites the conceptual model of a thermal boundary layer immediately above the seafloor explains many of the temporal and spatial temperature variations observed within a single vent field the thermal boundary layer is a lens of warm water injected from beneath the seafloor that is mixed and distended by lateral near bottom currents the volume of the boundary layer is delineated by the position of mature communities of sessile e g tubeworms and relatively slow moving organisms e g mussels vertical flow rates of hydrothermal fluids exiting the seafloor at diffuse vents are less than lateral flow rates of near bottom currents 5 10 cm s the presence of a subsurface shallow reservoir of warm hydrothermal fluids can explain differing temperature behaviors of adjacent diffuse flow and focused flow vents at 9 50 n different average temperatures and daily temperature ranges are explained by variable amounts of mixing of hydrothermal fluids with ambient seawater through subsurface conduits that have varying lateral permeability

the waihi epithermal gold silver base metal sulfide quartz vein system new zealand temperature and salinity controls on electrum and sulfide deposition the large andesite hosted quartz vein system at waihi contains a major epithermal au ag deposit total production of 6 4 moz au and 39 9 moz ag ag au 6 2 it is notable for a large vertical extent up to 575 m of economic au ag ore a pervasive adularia quartz illite chlorite pyrite alteration zone bounds the larger quartz veins and is associated with veinlets of quartz calcite pyrite adularia illite this zone is enveloped by an illite quartz adularia chlorite calcite pyrite alteration zone which grades out through a transition zone characterized by interlayered illite smectite into a smectite chlorite calcite alteration zone in the least altered andesites the formation of the adularia quartz chlorite calcite pyrite and some illite in these alteration assemblages was associated with an initial stage of vein filling by platy calcite and quartz this was followed by a main stage of quartz and sulfide vein filling with crustiform quartz at deeper levels and colloform quartz plus minor adularia at shallow levels deposition of main stage quartz and sulfides was accompanied by illite overprinting adularia in the wall rock and filling fractures in the quartz calcite pyrite adularia veinlets sulfide bearing bands associated with the main stage quartz show a zonation with decreasing depth from a coarse grained sphalerite galena pyrite chlorite assemblage at deep levels to a finer grained sphalerite galena pyrite chalcopyrite acanthite electrum assemblage at medium to shallow levels fluid inclusion studies indicate that the main stage quartz was deposited from fluids which ranged in temperature and composition from up to 295 c and 1 7 wt percent nacl equiv at depth to 190 c and 0 2 wt percent nacl equiv at shallow levels these are true salinities because the fluids extracted from the fluid inclusions have low co 2 contents 0 05 0 24 wt quartz within electrum poor zn pb fe sulfide bands was deposited at higher temperatures 295 242 c and salinities than quartz in electrum bearing zn pb fe cu ag sulfide bands 260 190 c temperature versus depth profiles for fluid inclusions with evidence of boiling indicate that the paleowater table was located about 160 m above the present erosion level during deposition of the main stage quartz minor amethyst as the final stage of vein filling was locally preceded by inesite and was not associated with sulfides and electrum amethyst was deposited at 253 to 170 c from fluids containing up to 4 5 wt percent nacl equiv these higher salinities are attributed to concentration of salts in the residual liquid by localized open system boiling chloride depth chloride enthalpy and 18 o water enthalpy plots indicate mixing of deep fluids up to 1 7 wt nacl for the main stage quartz with very low salinity steam heated ground water oxygen isotope 18 o values for vein quartz and amethyst range from 6 1 to 11 6 per mil and for vein calcite from 2 29 to 9 4 per mil calculated 18 o water values define a trend from 2 9 per mil at shallow levels to 0 6 per mil at depth extrapolation of the dilution trend on a 18 o water enthalpy plot indicates that the deep fluid 18 o water 0 6 was mixed with heated 160 180 c ground water of local meteoric water composition 5 5 dilution of a deep chloride fluid 1 2 wt nacl equiv carrying zinc and lead as chloride complexes with steam heated ground water is inferred to have been responsible for deposition of the electrum poor zn pb fe sulfide assemblage from 300 to 240 c at a paleodepth below about 500 m deposition of this assemblage may also have been promoted by decrease of sulfur in solution through loss of h 2 s gas by boiling during episodic fracturing the decrease in salinity following dilution favored the transport of gold silver and copper as hydrosulfide complexes and led to the deposition of the electrum bearing zn pb fe cu ag sulfide assemblage over a temperature range of 260 to less than 190 c at paleodepths of 500 to less than 250 m in this assemblage the decrease of sulfur in solution as a result of deposition of the associated chalcopyrite pyrite and galena is a likely mechanism for electrum deposition

hydrothermal activity on the reykjanes ridge the steinaholl vent field at 63 06 n we have completed a systematic survey for hydrothermal activity along the reykjanes ridge from 57 45 n to 63 09 n shipboard determinations of total dissolvable mn tdmn and dissolved si ch4 and h2 have revealed evidence for only one site of hydrothermal activity along this section of ridge crest the steinaholl vent field at 63 06 n 1 our measurements confirm this site to be a stable hydrothermal convection cell of at least two years duration the site is situated in just 250 350 m of seawater and unlike deeper sited vent fields e g tag 3650 m 26 n mar is notable for the formation of bubble rich plumes which have been imaged using a high frequency 38 khz echo sounder high dissolved gas concentrations of up to 18 nmol l ch4 and 30 nmol l h2 coincide with these bubble rich plumes the steinaholl plume is also characterised by high total dissolvable mn tdmn anomalies up to 60 nmol l and dissolved si anomalies 2 mol l yielding molar tdmn ch4 and tdmn si ratios of 3 5 and 0 03 respectively directly comparable to the tag hydrothermal plume the absence of any indication of hydrothermal activity along the remainder of the reykjanes ridge is intriguing between 11 n and 40 n on the mid atlantic ridge previous studies have revealed evidence for hydrothermally active sites approximately every 150 km for the 300 km of ridge crest studied in detail here 750 km total only one site has been found thus despite its proximity to the iceland hot spot the incidence of hydrothermal activity along this section of ridge crest appears to be only 20 50 of that measured elsewhere along the slow spreading mid atlantic ridge

quantifying diffuse and discrete venting at the tour eiffel vent site lucky strike hydrothermal field 1 the relative heat carried by diffuse versus discrete venting of hydrothermal fluids at mid ocean ridges is poorly constrained and likely varies among vent sites estimates of the proportion of heat carried by diffuse flow range from 0 to 100 of the total axial heat flux here we present an approach that integrates imagery video and temperature measurements to accurately estimate this partitioning at a single vent site tour eiffel in the lucky strike hydrothermal field along the mid atlantic ridge fluid temperatures photographic mosaics of the vent site and video sequences of fluid flow were acquired during the bathyluck 09 cruise fall 2009 and the momarsat 10 cruise summer 2010 to the lucky strike hydrothermal field by the rov victor6000 aboard the french research vessel the pourquoi pas ifremer france we use two optical methods to calculate the velocities of imaged hydrothermal fluids 1 for diffuse venting diffuse flow velocimetry tracks the displacement of refractive index anomalies through time and 2 for discrete jets particle image velocimetry tracks eddies by cross correlation of pixel intensities between subsequent images to circumvent video blurring associated with rapid velocities at vent orifices exit velocities at discrete vents are calculated from the best fit of the observed velocity field to a model of a steady state turbulent plume where we vary the model vent radius and fluid exit velocity our results yield vertical velocities of diffuse effluent between 0 9 cm s 1 and 11 1 cm s 1 for fluid temperatures between 3 c and 33 5 c above that of ambient seawater and exit velocities of discrete jets between 22 cm s 1 and 119 cm s 1 for fluid temperatures between 200 c and 301 c above ambient seawater using the calculated fluid velocities temperature measurements and photo mosaics of the actively venting areas we calculate a heat flux due to diffuse venting from thin fractures of 3 15 2 22 mw discrete venting of 1 07 0 66 mw and by incorporating previous estimates of diffuse heat flux density from tour eiffel diffuse flux from the main sulfide mound of 15 6 mw we estimate that the total integrated heat flux from the tour eiffel site is 19 82 2 88 mw and that the ratio of diffuse to discrete heat flux is 18 we discuss the implication of these results for the characterization of different vent sites within lucky strike and in the context of a compilation of all available measurements of the ratio of diffuse to discrete heat flux

intrusion hosted mineralization in the charters towers goldfield north queensland new isotopic and fluid inclusion constraints on the timing and origin of the auriferous veins auriferous quartz sulfide veins of the charters towers goldfield are mainly hosted in oxidized i type granitoids of the ravenswood batholith k ar and ar ar isotope age data of hydrothermal muscovite from alteration envelopes of veins at charters towers and the hadleigh castle mine 40 km east of charters towers are indistinguishable within error suggesting broadly synchronous gold deposition between 410 and 404 ma and across a significant segment of the ravenswood batholith published geochronological data indicate that several granitoid bodies were emplaced into the ravenswood batholith at the time of gold mineralization despite their association in space and time with igneous rocks the gold deposits lack an obvious causative intrusion moreover published lead isotope studies indicate that the lead in the ore was not acquired from any of the exposed intrusions a distal origin of the ore forming fluids also may be inferred from nitrogen isotope values of hydrothermal sericite suggesting wall rock interaction with metamorphic fluids or fluids that were in equilibrium with metamorphic rocks during the paragenetic stage of pyrite and arsenopyrite deposition stage ii veins of the charters towers goldfield contain three different types of fluid inclusions which are distinguishable by petrography and microthermometry this study is the first to report saline fluid inclusions in sphalerite 18 9 28 3 wt nacl equiv and vein quartz 20 9 24 7 wt nacl equiv trapped during the stage of gold deposition stage iii the range of temperatures and salinities particularly of the saline inclusions in sphalerite could indicate mixing between hotter more saline fluids e g deep seated magmatic and cooler more dilute solutions e g modified meteoric as the cause of gold deposition the geological and geochemical data are not compatible with derivation of fluids metals and ligands from individual plutons similarity of host rocks ore element associations alteration assemblages structural controls and tectonic settings strongly suggest that the auriferous veins of the charters towers goldfield belong to a group of granitoid hosted lode gold deposits that are generally classified as orogenic

porphyry gold deposits of the refugio district maricunga belt northern chile the porphyry gold deposits of the refugio district and similar deposits in the maricunga belt contain the lowest known copper to gold ratios cu ppm au 0 03 of any porphyry type deposit the gold deposits are associated with subvolcanic andesitic to dacitic intrusions emplaced into coeval volcanic rocks both the verde and pancho deposits are zoned in space from a deeper zone of banded quartz veinlets associated with chlorite magnetite albite and or pyrite albite clay alteration to a shallow zone of pyrite albite clay and local quartz alunite ledges pancho contains an additional deepest porphyry copperlike zone with quartz veinlets a veinlets and potassic alteration relative to verde pancho is telescoped with all three zones present within a 400 m vertical interval the porphyry copperlike zone at pancho is characterized by a veinlets and pervasive potassic alteration both restricted to intrusive rocks a veinlets range from hairline streaks of magnetite biotite with minor quartz and chalcopyrite and k feldspar alteration envelopes to sugary quartz veinlets 1 cm in width with magnetite and chalcopyrite and no alteration envelopes hypersaline liquid inclusions coexisting with vapor rich inclusions indicate temperatures above 600 c and salinities as high as 84 wt percent nacl equiv a pressure estimate of 250 bars indicates a depth of 1 000 m assuming lithostatic pressure potassic alteration consists of a central zone of magnetite k feldspar oligoclase that changes outward to a biotite rich zone total sulfide content predominately as chalcopyrite is generally 1 vol percent whereas magnetite content is 2 to 5 percent where a veinlets and potassic alteration predominate grades are typically 0 1 wt percent hypogene copper and 0 5 to 1 ppm gold banded quartz veinlets are present at both verde and pancho where they occur mostly above a veinlets and cut a veinlets where they overlap they are less than 2 cm in thickness and lack alteration envelopes dark gray bands whose color is due to abundant vapor rich fluid inclusions and micrometer sized grains of magnetite commonly occur as symmetric pairs near the vein walls the bands are commonly botryoidal and are continuous through quartz grains suggesting that the quartz recrystallized from a silica gel rare liquid rich fluid inclusions in quartz indicate temperatures 350 c and salinities 35 wt percent nacl equiv estimated pressures are 200 bars suggesting depths of 190 to 1 500 m under hydrostatic pressure gold occurs both in the dark bands with magnetite and outside the dark bands with pyrite chlorite illite and k feldspar banded veinlets occupy steeply dipping radial and shallowly dipping concentric fractures zones of abundant banded veinlets without early a veinlets generally contain 0 5 to 2 ppm gold and 0 05 wt percent hypogene copper most of the differences between porphyry gold deposits at refugio and porphyry copper deposits can be attributed to shallower depths of formation less than 1 km compared to 1 5 to 4 km that is typical for porphyry copper deposits shallower depths resulted in lower sulfide concentrations local garnet veinlets widespread albite bearing alteration and most importantly banded quartz veinlets which are unique to porphyry gold deposits banded quartz veinlets are a direct result of episodic intrusion of magma to within 1 km of the surface and exposure of high temperature magmatic fluids to hydrostatic pressures episodic rupturing of a brittle ductile boundary surrounding the intrusive centers at verde and pancho led to flashing of magmatic fluids loss of sulfur to vapor and low sulfide gold ratios in ore

lode gold and epithermal deposits of the mallina basin north pilbara terrain western australia the mallina basin in the central west part of the north pilbara terrain is one of the more mineralized parts of the pilbara craton three styles of au mineralization are present in the region 1 lode au deposits associated with sericite carbonate pyrite alteration assemblages 2 lode au deposits associated with pyrophyllite bearing alteration assemblages and 3 lode sb au deposits gold resources have been identified at the withnell and camel deposits just to the north of the east trending mallina shear zone east trending mineralized zones at the withnell deposit are typical of turbidite hosted lode au deposits in that they are late tectonic syn to late local d3 and associated with extensive carbonate sericite alteration gold mineralization occurs in planar quartz carbonate veins and with pyrite and arsenopyrite in the host rocks to the veins fluid inclusion analyses indicate mainly low salinity carbonic inclusions with moderate homogenization temperatures the lode sb au deposits have a similar structural setting and fluid characteristics at the camel 2 deposit au is associated with syn to late d3 pyrophyllitic shear zones that have overprinted an earlier carbonate alteration assemblage structural relationships and limited pb isotope data suggest that the lode au mineralization in this district formed at about 2900 ma in addition to the lode au and sb au deposits north northwest trending quartz veins have textures typical of low sulfidation epithermal deposits the lithogeochemistry of samples collected from these veins indicates local enrichment of au as sb ag te and hg which is consistent with an epithermal origin based on geologic relationships and pb isotope data these deposits are interpreted to have formed in the mallina basin at ca 2750 ma if they are true epithermal deposits then they are among the oldest known their presence suggests that preservation not archean age is the key control on the temporal distribution of epithermal deposits

mathematical modeling of diffuse flow in seafloor hydrothermal systems the potential extent of the subsurface biosphere at mid ocean ridges abstract we describe a variety of one and two dimensional mathematical modeling approaches to characterizing diffuse flow circulation at mid ocean ridge hydrothermal systems the goal is to estimate the potential extent of the sub seafloor microbial biosphere based on subsurface contours of the 120 c isotherm as determined from the various models the models suggest that the sub seafloor depth for microbial life may range from less than 1 m in some places to the thickness of crustal layer 2a of 500 m in others this depth depends primarily on how diffuse flow is driven the 120 c isotherm tends to be much deeper if diffuse flow is induced as boundary layer flow near high temperature plumes than if it results from conductive cooling or mixing near the seafloor because the heat flow alone may not allow identification of the flow regime in the subsurface we highlight the use of chemical tracers as an additional constraint that sheds light into the flow and reaction patterns associated with vents we use thermodynamic modeling which connects the temperature of the diffuse fluid to its chemical composition as the temperature composition relationships differ for mixing versus conductive heating and cooling the fluid geochemistry can shed light on subsurface transport using methane as an example the geochemical models indicate subsurface microbial methane production and consumption in different regions of the vent field near epr 9 50 n

characteristics and origin of archean premetamorphic hydrothermal alteration at the campbell gold mine northwestern ontario canada the campbell mine located in northwestern ontario canada is developed within a metamorphosed and deformed fault controlled archean gold deposit hosted predominantly within basalt and ultramafic rocks with lesser quantities of rhyolite and diorite the sequence of hydrothermal alteration has been subdivided into three partially overlapping phases consisting of an early alteration phase followed by the main stage vein phase and culminating in the mineralization phase early alteration consists of two substages represented by carbonatization and pervasive biotite potassic alteration and early silicification and aluminosilicate bearing alteration carbonate alteration is relatively wide spread whereas biotitic alteration occurs proximal to alteration controlling structures in highly carbonatized and or silicified rocks carbonate biotite alteration grades into carbonate chlorite alteration laterally outward

evolution of the peak hill high sulfidation epithermal au cu deposit eastern australia the early palaeozoic macquarie arc southeastern australia hosts a variety of major late ordovician to earliest silurian subduction related deposits e g cadia east ridgeway cadia hill cowal and northparkes however there is uncertainty about whether coeval high sulfidation epithermal deposits which occur in intra oceanic metallogenic belts elsewhere in the west pacific e g lepanto and chinkuashih are also present in the macquarie arc this has led to suggestions that their absence may be due to the poor preservation potential of deposits that form at relatively shallow crustal levels in ancient rocks we present here an interpretation for evolution of the peak hill au cu deposit based on the distribution of alteration facies sulfur isotope data from several textural forms of pyrite and barite and an assessment of the regional volcanic and sedimentary facies architecture these data show that the peak hill deposit displays a distinct sub vertical zoning with a pyrophyllite and vuggy quartz core that today extends about 350 m east west and at least 550 m north south which grades out through paragonite muscovite kaolinite to a chlorite epidote alteration zone at the margin the alteration zoning reflects both lower temperatures and neutralisation of acid fluids with increasing distance from the core which represents the conduit along which hot acidic hydrothermal fluids were channelled several temporally overlapping events of silicification bladed quartz pyrite veining brecciation and pyrite veining occurred during the last stages of hydrothermal alteration although most appear to predate mineralisation au cu mineralisation was associated with late quartz pyrite barite veins and the highest gold grades occur mainly in microcrystalline quartz altered rocks in the paragonite muscovite alteration zone generally within 50 m outward from the boundary of the pyrophyllite and vuggy quartz core sulfur and lead isotope data and the characteristic zoning of ore minerals and alteration assemblages support a magmatic source for the hydrothermal fluids similarities in many of the isotopic signatures between peak hill and deposits such as northparkes support generation of the high sulfidation mineralisation during the late ordovician to earliest silurian possibly ca 440 ma metallogenic event the late ordovician to early silurian volcanic and sedimentary facies associations at peak hill are consistent with alteration and mineralisation occurring in rocks deposited in a submarine setting

complementary acoustic and optical methods for characterization of diffuse venting gas seeps and biota distributions at hydrothermal systems a case study at kick em jenny volcano grenada west indies abstract quantitatively assessing the impact of hydrothermal circulation on geological and biological systems in submarine environments requires accurate characterization of biota fluid flow and in many shallow systems gas discharge in a single vent field surface expressions of hydrothermal venting and vent biology are often widespread presenting a significant technical challenge to such characterizations typically attempts to overcome this challenge involve extrapolation of point measurements to estimate field scale parameters extrapolation introduces large uncertainties however we present a case study at the kick em jenny volcano grenada west indies that jointly applies a set of complementary acoustic and optical measurement methods to significantly reduce uncertainty in field scale flux estimates of diffuse venting bubble streams and distributions of microbial mats two classes of rov based methods are used 1 survey level techniques for accurately locating fluid and gas discharge across entire vent fields and 2 local techniques that accurately measure fluid or gas fluxes just above a vent orifice survey level techniques include a structured light laser system to locate active diffuse venting and biological mats and a high resolution downward facing multibeam system that can resolve individual bubble streams separated by only centimeters local techniques include processing of stereo imagery to determine bubble stream parameters rise rate bubble size and application of the diffuse flow velocimetry technique to determine upwelling rates of diffuse effluent joint application of these methods provides a several times increase in the number of identified bubble streams relative to ship board systems and a difference of up to 40 times in field scale diffuse volume flux estimates relative to currently available techniques

hydrologic implications of alteration and fluid inclusion studies in the fresnillo district mexico evidence for a brine reservoir and a descending water table during the formation of hydrothermal ag pb zn orebodies ag pb zn mineralization in the fresnillo district formed from a large magma related hydrothermal system between approximately 32 to 28 ma a partial record of this hydrothermal activity is preserved by hydrothermal alteration mineral assemblages and fluid inclusions occurring in barren and mineralized parts of the district these features provide constraints on the hydrologic interpretation of the mineralizing system surficial exposures contain alteration assemblages which reflect two distinct fluid types that are known to occur in the shallow parts of active hydrothermal systems the hydrothermal mineral assemblage comprising quartz calcite illite or interlayered illite montmorillonite plus or minus chlorite pyrite or adularia occurs in scattered exposures around the district and indicates the former widespread presence of near neutral ph chloride waters fluid inclusion data in barren exposures south of the district center indicate that these fluids were dilute containing less than 5 wt percent nacl equiv and had temperatures in the range of 160 degrees to 240 degrees c the assemblage of kaolinite plus or minus alunite and natroalunite occurs locally above blind orebodies in the southern part of the district and in outlying exposures and indicates the former presence of acid sulfate waters geologic and fluid inclusion evidence strongly suggests that these waters originated as steam heated condensates which formed above the water table at plateros which lies north of fresnillo a hotter thermal environment is exposed where fluid inclusion data range from 220 degrees to 300 degrees c in contrast to other surficial exposures in the fresnillo district those that crop out in the center of the district on cerro proano contain significant silver mineralization associated with stockwork quartz veins fluid inclusion data from two quartz crystals indicate part of a complex hydrothermal history in which fluids of 17 10 and 200 degrees c this last feature explains why the tops of late formed orebodies are concealed at 150 to 200 m depth this model implies that dilute hydrothermal fluids devoid of ore metals were the fluids mostly responsible for hydrothermal alteration and vein fillings at the present day surface and that changes to the hydrology significantly altered the position of the ore depositional environment

relationships between hydrothermal activity and axial magma chamber distribution depth and melt content 1 hydrothermal activity especially high temperature discharge is commonly thought to require the presence of an axial magma chamber amc but this association has not been examined systematically the availability of six lengthy 170 560 km ridge sections with continuous surveys of both amcs and hydrothermal plumes now makes it possible to quantitatively compare the distribution and intensity of hydrothermal activity to amc extent depth and at a few locations melt content these six ridge sections span spreading rates from 55 to 145 mm a and total 20 second order segments at the section multisegment scale the linear incidence of hydrothermal plumes increases with amc incidence amci r2 0 64 excluding the hot spot affected galapagos spreading center for all six sections plume incidence increases as amc depth below the seafloor decreases amcz r2 0 66 at the second order segment scale plume incidence is poorly correlated with both amci r2 0 12 and amcz r2 0 25 finally at the subsegment or local scale 0 75 km long bins plume intensity increases as amcz shallows r2 0 85 of bins where plumes are most intense and thus closest to their seafloor sources 68 13 lie directly over an amc as do at least 37 of the 40 known high temperature vent fields the data also allow tests of other hypotheses linking amc properties and hydrothermal activity existing data though still sparse do not support the hypothesis that lenses of melt rich magma preferentially support vigorous long lasting venting also the suggestion that increased hydrothermal cooling within a segment locally depresses amcz finds no support within any ridge section evidence for magma bodies is much scarcer on slow spreading ridges but the data are nevertheless consistent with those from faster ridges observations from all spreading rates thus demonstrate that high temperature vent fields are almost universally associated with the presence or inference of magma hot rock or other nonmagmatic heat sources are insufficient

the hemlo gold deposit ontario canada principal deposit characteristics and constraints on mineralization abstract the archean world class hemlo lode gold deposit has been overprinted by deformation and metamorphism resulting in part in several proposed depositional models for its emplacement no single model clearly accounts for all of the characteristics of the deposit most proposed models are inappropriate in terms of timing with respect to host rock deformation intrusion or metamorphism or require inappropriate geometry metal tenors or metal ratios the deposit is spatially associated with high strain zones a restraining bend in the hemlo greenstone belt and the volcanic sedimentary contact of the moose lake volcanic complex mlvc the restraining bend correlates with changes in the style of mineralization and or alteration hence the deposit is subdivided into two segments the west segment is west striking and consists of numerous low grade erratically mineralized west to west northwest striking zones mineralization is locally dominantly fracture controlled or disseminated the main segment strikes approximately 290 contains the majority of the ore and consists of two main tabular zones of dominantly disseminated mineralization the main mineralized zone within the lake superior shear zone and the lower mineralized zone within the moose lake fault zone a broad zone of alteration about 4 km long and as much as 400 m wide asymmetrically surrounds the deposit there is ample evidence at a variety of scales of d 2 structural control on the various mineralized zones tabular zones of alteration and or disseminated mineralization are parallel to the predominant s 2 fabric in the west segment and a composite mylonitic s 2 s 2m s 3c fabric in the main segment tabular mineralized zones of fracture controlled alteration and pervasive alteration are paraconcordant with lithotectonic units the deposit is ductilely deformed by d 2 and d 3 strains which are associated with sinistral and dextral transpression respectively the deposit was emplaced after f 2 folding synchronous with the incipient development of high strain zones during mid d 2 strain post deposit overprinting by deformation and regional metamorphism has resulted in remobilization and modification of some of the original deposit characteristics the hemlo gold deposit is interpreted as an atypical mesozonal orogenic disseminated replacement stockwork deposit broadly synchronous with d 2 and middle stage granitoid plutonism prior to or synchronous with peak regional metamorphism and involving magmatic metamorphic fluids its emplacement is poorly constrained between 2694 and 2677 ma u pb systematics are consistent with field evidence for a history of protracted episodic progressive strain intrusive activity and an evolving hydrothermal system the chief emplacement controls specifically appear to have been the restraining bend competency contrast at a major lithologic contact and permeability in a fragmental unit with general more broadly developed steady state permeability in ductile zones enigmatic barite associated with the deposit is considered an intrinsic product of the hydrothermal system the orientation of the major part of the deposit is consistent with statistically preferred orientations for large gold deposits in other gold camps of the superior province other examples of alteration and mineralization in the hemlo greenstone belt share some common attributes with the hemlo deposit these factors provide a basis for selecting favourable exploration targets in the greenstone belt

tidally driven effluent detected by long term temperature monitoring at the tag hydrothermal mound mid atlantic ridge abstract during aug 13 21 1994 temperatures and current velocity were simultaneously monitored on the tag hydrothermal mound three giant kelps gks vertical thermistor arrays of 50 m height were moored on the periphery of the central black smoker complex cbc a manatee multi monitoring system including current velocity was deployed 50 m east of cbc four daibutsu geothermal probes penetrated the sediment south to west of cbc compilation of all data revealed semi diurnal variations in water temperatures and current velocity and allowed us to discuss the source of these anomalies temperature anomalies of gks correlate well with current velocity and are interpreted to be caused by the main plume from cbc that was bent over by the tidal current we identified two types of asymmetric periodic temperature variations at daibutsu probes 2 and 8 located 20 m to the south of cbc by comparing temperatures and current velocity they are attributed to non buoyant effluents laterally advected by the tidal current the source of one variation is located east to ese of the probes and the source of the other is located to the north on aug 31 a new periodic anomaly emerged on probe 2 with its amplitude up to 0 8 c the 6 h offset between the new anomaly and the previous one suggests that the source of the new anomaly lies to the west of probe 2 the heat flux of these non buoyant effluents is estimated to range from 30 to 100 kw m 2 which is of the same order as direct estimates of diffuse flow at the tag mound it suggests that a significant amount of diffuse effluent is laterally advected by the prevailing current near the seafloor

origins of calcite in a boiling geothermal system the formation of hydrothermal calcite relates to the movement of carbon dioxide in a geothermal system as governed by boiling dilution and condensation in this paper we show how these processes control the occurrence distribution and stable isotope composition of calcite based on a study at broadlands ohaaki the two principal calcite occurrences in the broadlands ohaaki geothermal system are 1 as replacement of rock forming minerals and volcanic glass and 2 as platy crystals infilling voids both are stable over a broad temperature range from 160 degrees c to 300 degrees c replacement calcite is widespread and forms through hydrolysis reactions involving calcium alumino silicates and sub boiling liquids that contain 0 3 to 0 75 m co 2 platy calcite in contrast forms over a restricted vertical interval of a few hundred meters within the upflow zone it precipitates from boiling fluids through exsolution of carbon dioxide as indicated by coeval liquid rich and vapor rich fluid inclusions and its formation in the two phase zone fluid inclusion data help to define the boiling paths of fluids from which platy calcite formed homogenization temperatures range from 160 degrees c to 310 degrees c and are consistent within the present geothermal regime ice melting temperatures range from 0 0 to 1 0 degrees c and indicate the presence of up to 0 5 m dissolved carbon dioxide model boiling curves calculated to match these data show how the concentration of dissolved carbon dioxide in the preboiled fluid dictates the depth of first boiling most fluid inclusion data lie along a model boiling path characteristic of the centre of the upflow zone in which the rising fluid initially containing 0 75 m co 2 begins to boil at approximately 320 degrees c and approximately 2000 m depth data from well br 18 instead matches a curve in which the rising fluid initially containing 0 53 m co 2 begins boiling at approximately 245 degrees c and approximately 900 m depth the shallowing of the depth of first boiling likely results from dilution of dissolved carbon dioxide in the parent chloride water as it rises and mixes with marginal waters calcite precipitates from both shallow formed steam headed groundwater and deeply derived chloride water and these waters are isotopically distinct at broadlands ohaaki the delta 18 0 values of calcite at 200 degrees c range from 0 5 to 7 5 per mil whereas delta 18 0 values of calcite at 200 degrees c range from 4 to 10 per mil taking appropriate temperature dependent fractionation factors into account these data indicate equilibration with chloride water delta 18 0 h2o 4 5 per mil and steam heated groundwater delta 18 o h2o 7 0 per mil respectively oxygen isotopes of hydrothermal calcites in the nearby wairakei and waiotapu geothermal systems show similar patterns consistent with the occurrence of both chloride and steam heated waters there calcite formation is explained by a model that describes the distribution of two phase conditions and aqueous carbon dioxide concentrations in a column of hydrothermal fluid rising through a rock matrix of isotropic permeability in this ideal situation platy calcite forms along the inner margin of the two phase zone having the shape of an inverted cone whereas replacement calcite mostly forms in the surrounding one phase liquid only zone the sparse occurrence of calcite at less than or equal to 800 m depth in the central upflow of the ohaaki sector at broadlands ohaaki is compatible with this model and appears related to the exsolution of dissolved carbon dioxide through boiling deeper in the system

crustal magnetization and the subseafloor structure of the ashes vent field axial seamount juan de fuca ridge implications for the investigation of hydrothermal sites

discrete and diffuse heat transfer atashes vent field axial volcano juan de fuca ridge abstract heat fluxes of discrete and diffuse components of hydrothermal discharge are estimated from submersible measurement in the ashes vent field located in the caldera of axial volcano on the central juan de fuca ridge the discrete component comprises discharge from individual vents and the diffuse component comprises seepage from large areas of the seafloor the investigation centered on the high temperature portion of the field a 100 100 m area of fractured lobate and sheet lava flows encompassing discrete discharge 326 c from seven individual vents and diffuse flow from intervening areas a total of 4 4 2 10 6 w was estimated for the discrete heat flux based on measurements of effluent temperature flow rate and orifice diameter at all the known individual vents by d s v alvin in september 1987 a total of 15 75 10 6 w was calculated with a standard plume model for the diffuse flux based on a grid of temperature measurements at altitudes of 1 m and 20 m above the study area using a 1 m long vertical array of temperature sensors mounted at the front of alvin s instrument platform the study indicates that 1 the diffuse component rises separately from the discrete component of hydrothermal discharge and is laterally advected by a prevailing current below the discrete component and that 2 the diffuse component of convective heat flux is approximately an order of magnitude greater than the discrete component in the high temperature portion of the ashes vent field

predicting gold rich epithermal and porphyry systems in the central andes with a continental scale metallogenic gis brgm s gis andes a comprehensive continental scale metallogenic information system for the entire andes cordillera is based on original syntheses structured into thematic layers the aim of developing the gis was to produce an integrated tool to understand ore deposit localization in the andes a fundamental question arising at the outset was whether the tool would be suitable for producing predictive mineral resource maps at the continental scale considering that previous predictive studies focus only on the regional scale the continental scale synthesis implied working with heterogeneous data in terms of distribution quantity quality and in particular accuracy the benefit is the ability to include uncommon parameters linked to the geodynamic evolution of the active margin and significant only at the continental scale in view of the particularities of the gis dataset an expert guided data driven approach was adopted for the multicriteria processing an approach that combined expert knowledge and the use of elementary statistics allowing to provide a link between the tectonic development of the whole andean margin and the spatial and temporal distribution of individual mining districts this study was purposely restricted to assessing the distribution of neogene gold in the central andes between lat 3 and 33 s thus a incorporating well constrained data on the present morphology of the convergent margin and b avoiding ambiguities in the less well constrained older history of the complex evolution of the andean margin five regional parameters were selected and were considered to have a significant influence on the neogene magmatic hydrothermal ore formation at continental scale the five parameters i host rock lithostratigraphy ii lithostratigraphic contacts iii structural discontinuities and iv depth and v dip of the wadati benioff zone modeled from seismic data had assigned favorability scores from 0 to 2 based on their associated metal content with respect to a set of identified neogene gold deposits the next step was to calculate favorability maps for each criterion that were combined to create an overall cumulative favorability map or predictive gold map verifying the predictive map against known gold deposits it was found that the cumulative favorability score of 4 out of 10 maximum located about two thirds of the known gold bearing epithermal and porphyry deposits and 95 of the metal content a cumulative favorability score of 5 reduced these figures to 50 of the deposits and 71 of the metal content and that of 6 relocated 24 of the deposits and 51 of the metal content in addition to verifying the method the predictive map outlines new potentially favorable gold areas and even indicates that some known districts could well host yet undiscovered mineralization

temporal variations in diffuse hydrothermal flow at tag we have obtained direct measurements of diffuse hydrothermal effluent temperature velocity and chemistry from the tag hydrothermal mound 26 08 n 44 49 w mid atlantic ridge we report on the time series physical measurements obtained from a location on the eastern flank of the main summit complex several features were observed including strong tidal variability in flow a conspicuous elevation of effluent temperatures during the period 11 october 17 october 1994 and a long term increase in temperature superimposed upon all other trends the six day long temperature excursion is coincident with increases in sediment and effluent temperatures observed by instruments left in place on the tag mound by other workers we have established through time lapse seafloor video observations and through drilling records that the mid october effluent temperature excursion is correlated closely with local drilling activity by the ocean drilling program

structure temporal evolution and heat flux estimates from the lucky strike deep sea hydrothermal field derived from seafloor image mosaics 1 here we demonstrate with a study of the lucky strike hydrothermal field that image mosaicing over large seafloor areas is feasible with new image processing techniques and that repeated surveys allow temporal studies of active processes lucky strike mosaics generated from 56 000 images acquired in 1996 2006 2008 and 2009 reveal the distribution and types of diffuse outflow throughout the field and their association with high temperature vents in detail the zones of outflow are largely controlled by faults and we suggest that the spatial clustering of active zones likely reflects the geometry of the underlying plumbing system imagery also provides constraints on temporal variability at two time scales first based upon changes in individual outflow features identified in mosaics acquired in different years we document a general decline of diffuse outflow throughout the vent field over time scales up to 13 years second the image mosaics reveal broad patches of seafloor that we interpret as fossil outflow zones owing to their association with extinct chimneys and hydrothermal deposits these areas encompass the entire region of present day hydrothermal activity suggesting that the plumbing system has persisted over long periods of time loosely constrained to hundreds to thousands of years the coupling of mosaic interpretation and available field measurements allow us to independently estimate the heat flux of the lucky strike system at 200 to 1000 mw with 75 to 90 of this flux taken up by diffuse hydrothermal outflow based on these heat flux estimates we propose that the temporal decline of the system at short and long time scales may be explained by the progressive cooling of the amc without replenishment the results at lucky strike demonstrate that repeated image surveys can be routinely performed to characterize and study the temporal variability of a broad range of vent sites hosting active processes e g cold seeps hydrothermal fields gas outflows etc allowing a better understanding of fluid flow dynamics from the sub seafloor and a quantification of fluxes

fluid evolution wallrock alteration and ore mineralization associated with the rodalquilar epithermal gold deposit in southeast spain at rodalquilar gold mineralization is found in late tertiary volcanic rocks of the sierra del cabo de gata and is related to a caldera collapse radial and concentric faults were preferred sites for gold deposition hydrothermal activity produced a specific alteration zoning around gold bearing vein structures grading from an innermost advanced argillic via an argillic into a more regionally developed propylitic zone advanced argillic alteration with silica pyrophyllite alunite and kaolinite extends down to several hundred m indicating a hypogene origin high grade gold mineralization in vein structures is confined to the near surface part of the advanced argillic alteration fine grained gold is associated with hematite jarosite limonite or silica at a depth of about 120 m the oxidic ore assemblage grades into sulfide mineralization with pyrite and minor chalcopyrite covellite bornite enargite and tennantite two types of fluids from different sources were involved in the hydrothermal system overpressured and hypersaline fluids of presumably magmatic origin initiated the hydrothermal system subsequent hydrothermal processes were characterized by the influx of low salinity solutions of probable marine origin and by interactions between both fluids deep reaching advanced argillic alteration formed from high salinity fluids with 20 30 equiv wt nacl at about 225 c near surface gold precipitation and silification are related to fluids with temperatures of about 175 c and 3 4 equiv wt nacl gold was transported as au hs 2 and precipitation resulted from boiling with a concomitant decrease in temperature pressure and ph and an increase in fo2 all features of the rodalquilar gold deposit reveal a close relationship to acid sulfate type epithermal gold mineralization

establishing a new era of submarine volcanic observatories cabling axial seamount and the endeavour segment of the juan de fuca ridge abstract at least 70 of the volcanism on earth occurs along the 65 000 km network of mid ocean ridge mor spreading centers within these dynamic environments the highest fluxes of heat chemicals and biological material from the lithosphere to the hydrosphere occur during volcanic eruptions however because underwater volcanoes are difficult and expensive to access researchers are rarely if ever in the right place at the right time to characterize these events therefore our knowledge is limited about the linkages among hydrothermal chemical and biological processes during seafloor formation and crustal evolution to make significant advancements in understanding the evolution of mor environments the united states and canada have invested in the first plate scale submarine cabled observatory linked through the global internet spanning the juan de fuca tectonic plate these two networks include 1700 km of cable and 14 subsea terminals that provide 8 10 kw power and 10 gbs communications to hundreds of instruments on the seafloor and throughout the overlying water column resulting in a 24 7 365 presence in the oceans data and imagery are available in real to near real time the initial experimental sites for monitoring volcanic processes include the mor volcanoes called axial seamount and the endeavour segment that are located on the juan de fuca ridge axial a hot spot influenced seamount is the most robust volcano along the ridge rising nearly 1400 m above the surrounding seafloor and it has erupted twice in the last 15 years in contrast the endeavour segment is characterized by more subdued topography with a well defined axial rift and it hosts one of the most intensely venting hydrothermal systems known a non eruptive spreading event lasting 6 years was documented at endeavour between 1999 and 2005 hydrothermal venting intensity chemistry and temperature as well as associated biological communities at both sites were significantly perturbed by the magmatic and intrusive events this paper presents the similarities and differences between the axial and endeavour volcanic systems and identifies reasons why they are ideal candidates for comparative studies the u s has made a 25 year commitment for sustained observations using the cabled infrastructure the highly expandable nature of submarine optical networking will allow for the future addition of novel experiments that utilize ever evolving advancements in computer sciences robotics genomics and sensor miniaturization comprehensive modeling of the myriad processes involved will continue to assimilate and integrate growing databases yielding a new understanding of integrated processes that create the seafloor in the global ocean basins

the flux of gold and related metals through a volcanic arc taupo volcanic zone new zealand we determined the concentrations of gold silver arsenic antimony and mercury in deep hydrothermal solutions 1 km depth 200 to 300 c from six geothermal systems and calculated their fluxes for a 250 km long segment of volcanic arc in the taupo volcanic zone new zealand the three orders of variation in the concentrations

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

a numerical model of hydrothermal cooling and crustal accretion at a fast spreading mid ocean ridge 1 there are two competing models for lower crustal accretion at fast spreading ridges in the gabbro glacier model all the lower crust solidifies in a magma lens at the dike gabbro boundary and then flows to its final level in the sheeted sill model the lower crust is formed by sills emplaced at a variety of depths we present a steady state numerical representation of the sill model that explicitly includes hydrothermal circulation the crust is accreted uniformly at the ridge axis at all depths and hydrothermal circulation occurs in crustal rocks that have cooled below a threshold temperature the results show that when the permeability exceeds a threshold value 4 10 14 m2 for a cracking temperature of 800 c and a uniform permeability hydrothermal circulation can cool the entire crust near the ridge axis producing vertical isotherms in the lower crust at lower permeabilities the properties of seawater lead to bimodal cooling with the lowermost crust cooling more slowly than shallower depths these results are reasonably consistent with studies of the seismic structure of the east pacific rise and of plagioclase crystal size distributions in gabbros from oman we infer that the sheeted sill model cannot be discarded on thermal grounds

predictive mapping for copper gold magmatic hydrothermal systems in nw argentina use of a regional scale gis application of an expert guided data driven approach and comparison with results from a continental scale gis geographic information systems giss are very useful tools for managing checking and organizing spatial information from many sources and of many types in thematic layers processing of these data enables exploration oriented giss to produce potential and predictive maps for a given commodity which constitute documents of real use in decision making integration of all information in a single reference system enables a better understanding of the parameters controlling a region s metallogeny in terms of both time and space but what scale should be used for developing a mineral exploration gis should preference be given to systems with high spatial resolutions scale 1 500 000 or to more general systems with scales of around 1 1 500 000 or 1 2 000 000 will the gain be worthwhile relative to the additional work generated by compilation at a higher scale in order to make greater use of previous predictive studies performed on gold rich epithermal and porphyry systems at the scale of the entire andes an expert guided data driven approach is now applied to a regional scale gis of nw argentina between the puna and the sierrras pampeanas where known deposits like bajo de la alumbrera agua rica and others account for a metal potential of over 10 mt cu and 750 t au in developing this new predictive map three criteria that were likely to be connected to the mineralizing event were selected and quantified i lithostratigraphy because of its role as a favourable environment for the development of mineralization based on its physico chemical properties ii lithostratigraphic contacts based on the rheological properties of the formations in contact and iii the orientation of structural discontinuities which channel source magmas and encourage the circulation of hydrothermal fluids assigning a score enables classification of the favourabilities calculated for each of the criteria considered this approach is employed here to check and standardize the statistical results obtained by methods such as weight of evidence modelling or an algebraic approach for each criterion four classes were distinguished very favourable score 3 favourable score 2 slightly favourable score 1 and unfavourable score 0 the predictive map is obtained by adding the scores for the three favourable criteria defined above the regional scale work identified 20 anomalous envelopes with cumulative scores greater than 5 they correspond to mining areas that are active e g bajo de la alumbrera under development e g agua rica or abandoned e g la mejicana or to new areas e g the vicuna pampa volcanic complex structural analysis of the region integrating the orientation of the favourable envelopes suggests that the mineralizing fluids were emplaced under extensional conditions sub parallel to the principal directions of shortening i wnw ese found along the southern edge of the puna and ii e w seen in the sierra de famatina it appears that a regional scale information system is a tool that is well suited to the definition of areas for mineral prospecting and to the study and confirmation of metallotects usable for mineral exploration comparison with work conducted on the basis of a 1 2 000 000 geological compilation shows that the principal mining districts can indeed be found at continental scale on the other hand the lack of detail inherent at a scale of 1 2 000 000 may lead to inaccuracies in particular fictitious favourabilities assigned to formations that are genetically unrelated to the mineralization but that contain for example small tertiary intrusive bodies that cannot be recorded at this scale this comparison therefore shows that the use of a continental scale gis is effective and well suited to the definition of prospective areas at a strategic level

evaluation of the role of sulfidation in deposition of gold screamer section of the betze post carlin type deposit nevada this study was undertaken to evaluate the relation between sulfidation and gold deposition in the screamer section of the betze post carlin type deposit we also attempted to determine the source of sulfur in the deposit and the possibility that more than one gold depositing event contributed metal to the screamer system gold ore at screamer forms a generally stratiform body hosted largely by the wispy member of the devonian popovich formation and lacks obvious alteration of wall rock gangue minerals gold at screamer is hosted by arsenian pyrite that forms disseminated grains and overgrowths on diagenetic pyrite a strong correlation is observed between the gold content of rock samples and their proportion of ore related arsenian pyrite as determined by point counts isocon plots show that mineralization at screamer involved addition of both sulfur and iron along with gold arsenic antimony tungsten and local silica barium and phosphorus fe al vs s al plots show that most ore samples at screamer do not contain enough sulfur to account for all of their iron as pyrite petrographic examination shows that the iron occurs in pyrite ferroan dolomite and iron bearing micas in order of decreasing abundance the fe al vs s al plots also show that screamer samples with high gold contents contain more pyrite than samples with low gold contents and that samples inside the ore zone have more pyrite than those in the surrounding area these relations are interpreted to indicate that screamer has undergone at least two pyrite forming events the first event which probably took place during diagenesis involved incomplete sulfidation that left some iron in carbonate and silicate minerals the second event which probably took place during gold mineralization sulfidized most remaining iron and added pyrite in the screamer ore zone the 34 s values of chemically extracted sulfur from disseminated pyrite at screamer range from 13 8 to 16 5 per mil and 34 s values for hand picked separates of pyrite and other sulfides in veins cutting these rocks range from 21 2 to 11 7 per mil a significant fraction of samples with high gold contents and of samples in the ore zone regardless of gold content have 34 s values between 1 and 5 per mil these data suggest that early diagenetic sulfur with a wide range of 34 s values was overprinted by sulfur with isotopic compositions in the 1 to 5 per mil range that was associated with gold mineralization the 34 s values for gold related sulfur at screamer are lower than those reported for bulk mineral separates from most other carlin type deposits and from sims analyses of sulfides from the proximal post part of the betze post system and could be magmatic limited evidence can be found for multiple gold forming events in the screamer zone tungsten which might have been introduced by the jurassic age goldstrike stock is widespread in the deposit and correlates closely with gold a few samples with high tungsten gold ratios found along fault zones might be part of an earlier phase of mineralization related to the goldstrike stock a 34 s value for pyrite in one of these samples is similar to the high values reported for sulfides in auriferous polymetallic mineralization in the post section of the deposit but this mineralization is not reported to contain tungsten other veins containing sphalerite have lower 34 s values and lack consistent gold values whereas there is no correlation between gold values and the degree to which the host rocks have undergone sulfidation there is a strong and highly significant correlation between gold values and the abundance of ore related pyrite this shows that simple sulfidation of immediately adjacent wall rock cannot account alone for gold deposition at screamer and it might not be the only ore depositing process in some other carlin deposits a more general extended sulfidation process could be important however one likely process involves mixing of an invading mineralizing fluid containing sulfur and gold with a wall rock fluid containing iron derived from adjacent or distal wall rocks recognition of the source s for this iron and fluid flow pathways responsible for introducing it to the ore zone could provide useful guidance in exploration for the next carlin trend

postsubduction porphyry cu au and epithermal au deposits products of remelting of subduction modified lithosphere porphyry cu mo au and some epithermal au deposits are formed from hydrothermal fluids exsolved from cooling water rich calc alkaline magmas emplaced in volcanoplutonic arcs above subduction zones these magmas originate by partial melting of the metasomatized asthenospheric mantle wedge however there is increasing evidence for the existence of a suite of porphyry cu au and epithermal au deposits related to magmas generated after subduction beneath the arc has ceased associated magmas tend to be mildly alkaline relatively sulfur poor and emplaced as isolated complexes rather than in voluminous volcanoplutonic arcs they are likely formed by remelting of previously subduction modified arc lithosphere triggered by postsubduction lithospheric thickening lithospheric extension or mantle lithosphere delamination metasomatized mantle lithosphere or hydrous lower crustal cumulates residual from first stage arc magmatism contain small amounts of chalcophile and siderophile element rich sulfides and constitute a fertile source for hydrous au rich but relatively sulfur poor magmas during later remelting the recognition that porphyry cu au and related epithermal au systems can also form in postsubduction and collisional tectonic settings expands the range of geological environments and geographical terranes that are prospective for such deposits

resources of gold in phanerozoic epithermal deposits we have estimated earth s endowment of gold in phanerozoic epithermal deposits using a tectonic diffusion model which simulates the emplacement of deposits at a shallow crustal depth and their subsequent vertical tectonic migration in the crust the calculation was calibrated by least squares comparison of a calculated age frequency distribution to the age frequency distribution for 448 epithermal deposits of phanerozoic age results indicate that 17 percent of the epithermal deposits that formed through phanerozoic time remain in the crust today whereas 83 percent have been removed by erosion assuming a similar age distribution for all 1 181 epithermal deposits in our compilation indicates that 307 000 deposits formed throughout phanerozoic time that 63 000 of these remain in the crust and that 244 000 have been eroded grade and tonnage data of gold in 757 epithermal deposits in the compilation have an arithmetic average of 34 7 t and yield an estimate of 2 2 106 t of gold for epithermal deposits remaining in the crust using the model based vertical distribution of deposits remaining in the crust we estimate that epithermal deposits in the upper kilometer of the united states contain 2 9 104 t of gold adjusting for areas of outcropping volcanic rocks in each continent increases our estimate to 4 0 104 t these estimates are similar to the 1 7 104 t gold resource estimated by the u s geological survey using completely different methods several comparisons based on these results provide insights into the efficiency of processes that form epithermal deposits and the outlook for sustainability for instance all of the epithermal deposits that formed through phanerozoic time represent only about 0 03 percent of the gold in the crust only about 0 007 percent of crustal gold remains in epithermal deposits the rest has been eroded and recycled this is consistent with comparisons based on the flux of gold in the taupo volcanic zone which indicate that epithermal deposits trap only 0 1 to 0 2 percent of the gold that moves through convergent margin hydrothermal systems epithermal gold deposits that remain in the crust can supply current production from them for 1 400 to 5 000 years depending on success of exploration and depth of mining finally we are consuming gold from epithermal deposits about 17 000 times faster than earth is replenishing the supply

heat flux from black smokers on the endeavour and cleft segments juan de fuca ridge we have estimated the heat flux from black smoker vents on the juan de fuca ridge to evaluate their importance for heat transfer from young oceanic crust the velocity and temperature of smoker effluent were measured from the manned submersible alvin within a few centimeters of vent orifices using a turbine flowmeter with an attached temperature probe exit velocity was calculated from a simple plume model and vent orifices were measured in photographs and video records the estimated power output from smokers alone is 49 13 mw for the plume site vent 1 and vent 3 on the southern cleft segment near 45 n 364 73 mw for the main vent field on the endeavour segment near 48 n and 122 61 mw for the tubeworm field 2 km north the estimates for the cleft and tubeworm fields could be too low because of undiscovered vents these values constitute only 4 to 14 of the total advective heat flux estimated for these vent fields from measurements in the nonbuoyant plume and of diffuse flow at the seafloor indicating that most of the heat advected at these hydrothermal vent sites is carried by diffuse rather than focused flow values for individual smokers vary from 0 1 to 94 mw with an average of 6 2 mw at the endeavour field and 3 1 mw at the cleft field our estimates agree well at all scales with those of bemis et al 1993 based on measurements made during the same dives in some cases simultaneously up to 50 m high in the buoyant plume the good agreement between the two techniques implies that little diffuse flow at either high or low temperature is incorporated into the buoyant plumes generated by smokers at these sites velocity temperature measurements at vents excavated by alvin could not be modeled successfully suggesting that vent structures may grow in equilibrium with the force of the exiting water such that orifice size is determined by volume flux at the endeavour field the heat flux is focused by faults

synchronous advanced argillic alteration and deformation in a shear zone hosted magmatic hydrothermal au ag deposit at the temora gidginburg mine new south wales australia paragenetic relations indicate that advanced argillic alteration at the temora mine and the adjacent dam lilydale prospect is coeval with movement along shear zones which host each system the interaction between movement along the host structure and developing alteration zones of contrasting rheology controlled the flow of hydrothermal fluid and resultant overall system geometry neither of these systems represents older typical epithermal or porphyry related systems that were subsequently deformed however advanced argillic alteration at both prospects cuts across the peripheral parts of older porphyry style alteration systems with paragenetic relations analogous to the butte and dizon districts each system is characterized by an early phase of massive or breccia textured quartz dominated advanced argillic alteration cut by foliated mica rich quartz absent advanced argillic alteration phase relations indicate that early quartz saturated advanced argillic alteration developed at temperatures

seasonal variation of gravity wave activity at midlatitudes from 7 years of cosmic gps and rayleigh lidar temperature observations seven year series of gravity wave gw potential energy at midlatitude stratosphere 10 to 50 km is constructed by combining temperature profiles provided by constellation observing system for meteorology ionosphere and climate cosmic gps satellite constellation and rayleigh lidar operating at haute provence observatory in southern france the combined series are used to evaluate the representation of gw in modern era retrospective analysis for research and applications reanalysis the seasonal and zonal variabilities of gw activity are diagnosed using zonal wind and wind divergence provided by era interim reanalysis the spatiotemporal distribution of gw activity is found strongly dependent on the zonal wind variation wind divergence and topography we show that anomalies in the wind divergence can serve as a proxy for locating synoptic scale enhancements of gw the analysis provides evidence for orographic gw excitation and the results are compatible with geostrophic adjustment being an additional source of stratospheric gw the seasonal gw variability can be largely explained by interaction with the mean flow and wave propagation

tapping into the sub seafloor examining diffuse flow and temperature from an active seamount on the juan de fuca ridge abstract a unique sampling strategy involving the cementing of a permanent fluid sampler directly to the seafloor on axial seamount juan de fuca ridge has recently allowed the first long term direct coupling to a low temperature hydrothermal vent on a mid ocean ridge using the hydrologically sealed sampler direct measurement of fluid volume and heat flux from a diffuse hydrothermal vent on the seafloor was obtained over a period of 206 days enhanced variance at both tidal and lower frequencies was recorded with a high coherence between the temperature and flow data we estimate a volume flux of 48 m 3 yr and a heat flux of 260 w m 2 for the square meter of seafloor sampled by the instrument measurement of the darcy flow velocities of the effluent fluid are approximately 1 5 10 6 m s and indicate fluid velocities within cracks in the substrate of 1 4 m day with an effective upper crustal permeability of 10 11 10 12 m 2 while the measured variability in fluid flow is driven primarily by changes in the thermal buoyancy of upwelling fluid there is also a significant above hydrostatic pressure gradient contribution to the measured flux this overpressure produces roughly four times the driving force compared to that attributed to thermal buoyancy alone small variations in the volume flux and the effluent fluid temperature 1 5 10 8 m s and 0 5 c respectively also occurred on approximately tidal time scales and appear to be related to poroelastic control of the velocity of hydrothermal fluid through the seafloor boundary i e tidal pumping

advanced argillic lithocaps in the bolivian tin silver belt zones of advanced argillic alteration constituting lithocaps are commonplace in the shallow parts of porphyry copper systems similar lithocaps are also recognized in the shallowly eroded southern part of the bolivian tin silver belt where mineralization typically is centred on felsic volcanic domes a well preserved lithocap at potosi is dominated by vuggy residual quartz and contained the world s largest silver resource whereas the basal remnant of a lithocap at pulacayo is composed of barren quartz alunite minor gold occurs in the structurally controlled roots of a lithocap at tasna the mineralization in these lithocaps is of high sulphidation type and was generated in the epithermal environment in contrast the tin and base metal bearing massive sulphide veins and associated sericitic and quartz tourmaline alteration that underlie the bolivian lithocaps are typified by sulphides of low sulphidation state but are dominantly mesothermal rather than epithermal in character magma chemistry is believed to account for the characterization of bolivian lithocaps by silver tin antimony and porphyry copper lithocaps by gold copper arsenic low grade bulk tonnage silver mineralization within bolivian lithocaps and high grade tin bearing veins concealed beneath them both constitute attractive exploration objectives

the age and thermal history of cerro rico de potosi bolivia cerro rico de potosi bolivia is the world s largest silver deposit and has been mined since the sixteenth century for silver and for tin and zinc during the twentieth century together with by product copper and lead the deposit consists primarily of veins that cut an altered igneous body that we interpret to be a dacitic volcanic dome and its underlying tuff ring and explosion breccia the deposit is compositionally and thermally zoned having a core of cassiterite wolframite bismuthinite and arsenopyrite surrounded by a peripheral lower temperature mineral assemblage consisting principally of sphalerite galena lead sulfosalt and silver minerals the low temperature assemblage also was superimposed on the high temperature assemblage in response to cooling of the main hydrothermal system both the dacite dome and the ore fluids were derived from a larger magmatic hydrothermal source at depth the dome was repeatedly fractured by recurrent movement on the fault system that guided its initial emplacement the dome was extruded at 13 8 0 2 ma 2 based on u th pb dating of zircon mineralization and alteration occurred within about 0 3 my of dome emplacement as indicated by a 40ar 39ar date of 13 76 0 10ma 1 for sericite from the pervasive quartz sericite pyrite alteration associated with the main stage high temperature mineralization the last thermal event able to reset zircon fission tracks occurred no later than 12 5 1 1 ma 1 as indicated by fission tract dating minor sericite and magmatic steam alunite veins were episodically formed around 11 ma and between 8 3 and 5 7 ma the younger episodes occurring at the time of extensional fracturing at cerro rico and wide spread volcanism in the adjacent los frailes volcanic field none of these younger events appear to be significant thermal mineralizing events the exceptionally flat thermal release pattern of 39ar from sericite and the results of the fission tract dating of zircon show that none of the younger events was hot enough and lasted long enough to cause significant loss of ar or annealing of zircon fission tracks u th pb dating of zircon cores indicates a precambrian progenitor for some zircons and ree analyses of dated samples of hydrothermally altered dacite show the presence of a prominent positive eu anomaly which constrains interpretations of the origin and evolution of the magmatic hydrothermal system

late kinematic timing of orogenic gold deposits and significance for computer based exploration techniques with emphasis on the yilgarn block western australia abstract orogenic gold deposits are a widespread coherent group of epigenetic ore deposits that are sited in accretionary or collisional orogens they formed over a large crustal depth range from deep seated low salinity h2o co2 ch4 n2 ore fluids and with au transported as thio complexes regional structures provide the main control on deposit distribution in many terranes first order faults or shear zones appear to have controlled regional fluid flow with greatest ore fluid fluxes in and adjacent to lower order faults shear zones and or large folds highly competent and or chemically reactive rocks are the most common hosts to the larger deposits focusing of supralithostatic ore fluids into dilatant zones appears to occur late during the evolutionary history of the host terranes normally within d3 or d4 in a d1 d4 deformation sequence reactivation of suitably oriented pre existing structures during a change in far field stress orientation is a factor common to many deposits and repeated reactivation may account for multiple mineralization episodes in some larger deposits absolute robust ages of mineralization support their late kinematic timing and in general suggest that deposits formed diachronously towards the end of the 100 to 200 m y long evolutionary history of hosting orogens for example in the yilgarn block a region specifically emphasised in this study orogenic gold deposits formed in the time interval between 40 and 90 m y with most about 60 to 70 m y after the youngest widespread basic ultrabasic volcanism and towards the end of felsic magmatism the late timing of orogenic gold deposits is pivotal to geologically based exploration methodologies this is because the present structural geometries of i the deposits ii the hosting goldfields and iii the enclosing terranes are all essentially similar to those during gold mineralization at least in their relative position to each other thus interpretation of geological maps and cross sections and three dimensional models can be used to accurately simulate the physical conditions that existed at the time of ore deposition it is particularly significant that the deposits are commonly related to repetitive and predictable geometries such as structural heterogeneities within or adjacent to first order structures around rigid granitoid bodies or in specific locked up fold thrust structures importantly the two giant greenstone hosted goldfields kalgoorlie and timmins show a remarkably similar geometry at the regional scale computer based stress mapping and gis based prospectivity mapping are two computer based quantitative methodologies that can utilize and take advantage of the late timing aspect of this deposit type to provide important geological aids in exploration both in broad regions and more localized goldfields both require an accurate and consistent solid geology map stress mapping requires knowledge of the far field stresses during mineralization and the empirical prospectivity mapping requires data from a significant number of known deposits in the terrane the kalgoorlie terrane in the yilgarn block meets these criteria and illustrates the potential of these methodologies in the exploration for orogenic gold deposits low minimum stress anomalies interpreted to represent dilational zones during gold related deformation coincide well with the positions of known goldfields rather than individual gold deposits in the terrane and there are additional as yet unexplained anomalies the prospectivity analysis confirms that predictable and repetitive factors controlling the siting of deposits are i proximity to and orientation and curvature of granitoid greenstone contacts ii proximity to segments of crustal faults which strike in a preferred direction iii proximity to specific lithological contacts which have similar preferred strike iv proximity to anticlinal structures and v the presence of preferred reactive host rocks e g dolerite the prospectivity map defines a series of anomalous areas which broadly conform to those of the stress map 78 correspondence the most prospective category on this map covers less than 0 3 of the greenstone belts and yet hosts 16 of the known deposits which have produced 80 of known gold thus it discriminates in favour of the larger economically more attractive deposits in the terrane the successful application of stress mapping and prospectivity mapping to geology based exploration for orogenic gold deposits indicates that more quantitative analysis of geological map data is a profitable line of research the computer based nature of these methodologies is ideal for the production of an ultimate integrated deposit target map which can be compared to other more conventional targeting parameters such as geophysical and geochemical anomalies such an integrated strategy appears the way forward in the increasingly difficult task of cost effective global exploration for orogenic gold deposits in poorly exposed terranes

precious metal vein systems in the national district humboldt county nevada the national district 20 miles 33 km southeast of mcdermitt nevada produced 200 000 ounces of gold and 750 000 ounces of silver during the period 1906 1941 precious metal quartz sulfide silicate veins near the townsite of national and on buckskin mountain occur within a 3 000 ft thick 910 m sequence of miocene volcanic and intrusive rocks which vary in composition from basalt to rhyolite veins formed about 15 6 million years ago and associated rhyolites are approximately 18 to 15 m y old the volcanic pile at national is highly faulted and deposits are localized within orthogonal fault sets that coincide with major upper crustal structures in the northern great basin intrusive rhyolite and eruptive centers spatially related to veins at national partly define the goosey lake depression a shallow basin situated on the western edge of the owyhee volcanic plateau wall rock in the district is progressively hydrolyzed and sulfidized to assemblages dominated by chlorite calcite illite montmorillonite quartz pyrite and kaolinite quartz pyrite as veins are approached alteration assemblages exposed by exploration on buckskin mountain include the paleosurface at buckskin planar open space filled veins disperse upward into structurally unconfined flat lying zones of kaolinite quartz quartz alunite and chalcedonic silica sinter quartz altered rhyolite the latter being the paleosurface assemblage metallic minerals in four nested and coalescing vein stages include cinnabar stibnite electrum silver sulfosalts and selenides and base metal sulfides vein silicates are quartz kaolinite illite and at depth muscovite the spatial distribution of hydrothermal sulfides and silicates throughout buckskin mountain is strongly influenced by physical properties of premineralization volcanic rocks porous and permeable rhyolite tuff capping buckskin mountain is pervasively hydrolyzed to laterally extensive silica alunite and kaolinite bearing assemblages which lack tabular zones of open space filling underlying dense and brittle rhyolite flows confine hydrothermal assemblages to a relatively few planar fractures flanked by parallel selvedges of progressively altered wall rock at buckskin mountain two distinct but synchronous thermal events are documented by fluid inclusion studies the earlier event involved temperatures ranging from approximately 295 degrees to 250 degrees c and culminated in rupture of overlying rhyolite producing an inverted conical mass of bilithic breccia fluids associated with the second postbrecciation event boiled at 100 degrees to 255 degrees c from the paleosurface to depths exceeding 2 000 ft 606 m near surface hydrothermal assemblages were deposited from low salinity 1 2 wt nacl solutions containing 2 weight percent dissolved gases precious metal precipitation occurred at a temperature of about 250 degrees c and a pressure of about 40 bars largely from boiling solution periodic restrictions to convective heat loss resulting from silica deposition and episodic fluid circulation cause observed temperature and pressure data to deviate somewhat from an ideal hydrostatic model the vertical temperature gradient is consistent with a water saturated melt of granitic composition about 10 000 ft 3 030 m below the paleosurface during mineralization close spacing of isotherms below 200 degrees c reflects paleosurface proximity cooling by conduction and steam loss as well as accelerated convective cooling of fluid circulating through permeable rhyolite tuff integration of hydrothermal assemblages thermal measurements fluid mineral equilibria and active hot springs data suggests that as temperatures in buckskin mountain decreased from 250 degrees c at depth to 100 degrees c at the surface ph increased from approximately 3 7 to near neutral sigma s increased from 10 super 4 5 m to approximately 10 super 2 6 m and f sub o 2 decreased from 10 super 39 to 10 super 48 the distribution of alteration assemblages precious metal minerals stibnite and cinnabar was apparently controlled by boiling a sulfldation gradient temperature decreases and near surface hydrology

tidal pumping of fluids within and from the oceanic crust new observations and opportunities for sampling the crustal hydrosphere abstract seven boreholes established by the ocean drilling program in sedimented ridge crest and ridge flank environments have been sealed to stop the exchange of formation water and seawater via the holes after drilling and instrumented to allow long term hydrologic monitoring records of seafloor and basement fluid pressures in these holes document tidal frequency formation pressure variations that are attenuated and phase shifted relative to variations at the seafloor spatial variations in the response to seafloor tidal loading create oscillatory pressure gradients which drive fluid flow within the crust and tidal pressure differentials between the crust and the water column modulate flow through the seafloor both may have significant geochemical and biological consequences the magnitude of the tidal pressure differential observed across sediment sections is in many instances larger than the average differential pressure created by hydrothermal buoyancy forces and this causes the pressure difference across fluid sampling ports incorporated in the borehole seals to reverse sign periodically this can create a problem for obtaining undiluted crustal fluid samples at the seafloor from moderately overpressured holes but it also provides an opportunity for fluids to be pumped passively from moderately underpressured holes through the use of uni directional valves potential production rates estimated using pre and post seal thermal fluid flow and pressure data indicate that significant fluid fluxes can be established of the order of 10 m 3 typically one hole volume per month