the effect of crystal melt partitioning on the budgets of cu au and ag we have performed five separate sets of experiments to elucidate the effects of magnetite ulvospinel magnetite solid solution and pyrrhotite crystallization on the budgets of au cu and ag at magmatic conditions the experiments were done in both hydrous and anhydrous assemblages at temperatures between 800 and 1050 c pressures from ambient to 140 mpa log f o2 from nno 0 25 to nno and log f s2 from 1 5 to 3 0 nernst type partition coefficients 1 at 800 c in a water saturated assemblage are d agmt melt 2 10 4 2 10 9 d cumt melt 0 82 0 69 d cuusp melt 26 17 d auusp melt 50 31 d cupo melt 174 25 nernst type partition coefficients 1 at 1050 c in an anhydrous assemblage are d cupo melt 200 d agpo melt 58 8 d aupo melt 120 50 the calculated values for d auusp melt and d cuusp melt indicate that the addition of ti to magnetite increases significantly the au and cu scavenging potential of ulvospinel relative to end member magnetite partition coefficients for cu and au between pyrrhotite and melt indicate that a temperature change from 1050 to 800 c in an anhydrous and hydrous assemblage respectively results in no observable change in cu partitioning the calculated partition coefficients are used to model the effect of crystal fractionation on the concentrations of ag cu and au model results suggest that the co crystallization of magnetite and pyrrhotite sequester no more than 2 ag 7 cu and 37 au from the melt over the first 25 solidification if the melt reaches volatile saturation after 25 crystallization the presence of end member magnetite and pyrrhotite do not appear to inhibit the cu au and ag ore potential of the magma ulvospinel magnetite however may reduce the au concentration in the melt by approximately one third relative to its initial value that decreases the overall au available to partition into the volatile phase

assessing textural variation in laminated sands using digital image analysis of thin sections although between laminae parameter variations in sediments have been studied in the past measured parameters were generally limited to grain size distribution and total porosity the magnitude and directional characteristics of physical properties of laminated sediments also depend on the shape and orientation of particles packing pore size characteristics and properties of the pore network leaving out a complete characterization of granular sediment in models of physical properties could result in a systematic mismatch between modeled and measured values however tools for high resolution quantification of these spatial variable parameters are not readily available in order to provide such a tool an image analysis procedure is presented based on digital images of thin sections the procedure defines a sequence of rectangular measurement windows with their long sides oriented parallel to stratification and measures the sediment characteristics for each window logs of parameters values oriented perpendicular to stratification are thus created after verification of the image analysis procedure using comparative laboratory measurements the procedure is applied to two thin section images of unconsolidated fine grained laminated sands the quantitative variations observed in the logs of grain and pore characteristics correlate well with bedding observed on the original images overall the image analysis procedure proved to be a useful and versatile tool for quantifying variations of textural characteristics on sub lamina scale

magma evolution and the formation of porphyry cu au ore fluids evidence from silicate and sulfide melt inclusions silicate and sulfide melt inclusions from the andesitic farallon negro volcanic complex in nw argentina were analyzed by laser ablation icpms to track the behavior of cu and au during magma evolution and to identify the processes in the source of fluids responsible for porphyry cu au mineralization at the 600 mt bajo de la alumbrera deposit the combination of silicate and sulfide melt inclusion data with previously published geological and geochemical information indicates that the source of ore metals and water was a mantle derived mafic magma that contained approximately 6 wt h2o and 200 ppm cu this magma and a rhyodacitic magma mixed in an upper crustal magma chamber feeding the volcanic systems and associated subvolcanic intrusions over 2 6 million years generation of the ore fluid from this magma occurred towards the end of this protracted evolution and probably involved six important steps 1 generation of a sulfide melt upon magma mixing in some parts of the magma chamber 2 partitioning of cu and au into the sulfide melt enrichment factor of 10 000 for cu leading to cu and au concentrations of several wt or ppm respectively 3 a change in the tectonic regime from local extension to compression at the end of protracted volcanism 4 intrusion of a dacitic magma stock from the upper part of the layered magma chamber 5 volatile exsolution and resorption of the sulfide melt from the lower and more mafic parts of the magma chamber generating a fluid with a cu au ratio equal to that of the precursor sulfide 6 focused fluid transport and precipitation of the two metals in the porphyry yielding an ore body containing au and cu in the proportions dictated by the magmatic fluid source the cu s ratio in the sulfide melt inclusions requires that approximately 4 000 ppm sulfur is extracted from the andesitic magma upon mixing this exceeds the solubility of sulfide or sulfate in either of the silicate melts and implies an additional source for s the extra sulfur could be added in the form of anhydrite phenocrysts present in the rhyodacitic magma it appears thus that unusually sulfur rich not cu rich magmas are the key to the formation of porphyry type ore deposits our observations imply that dacitic intrusions hosting the porphyry cu au mineralization are not representative of the magma from which the ore fluid exsolved the source of the ore fluid is the underlying more mafic magma and unaltered andesitic dikes emplaced immediately after ore formation are more likely to represent the magma from which the fluids were generated at alumbrera these andesitic dikes carry relicts of the sulfide melt as inclusions in amphibole sulfide inclusions in similar dykes of other less explored magmatic complexes may be used to predict the au cu ratio of potential ore forming fluids and the expected metal ratio in any undiscovered porphyry deposit

on the dense bubble clouds and near bottom turbulence in the surf zone 1 measurements of high frequency 100 khz acoustical backscatter in the surf zone have identified the presence of a wall formed by dense assemblages of bubbles generated by breaking gravity waves and persisting for periods up to 30 min these bubbles are advected by alongshore and cross shore rip currents and are controlled by the local wave field turbulence dissolution and buoyancy during the summer of 2000 the location of the bubble wall south of scripps pier california was tracked for a 6 week period distinct categories of bubble wall defined by the backscatter intensity data are observed distinguished by the presence or absence of rip current activity the results suggest that presence or absence of long period waves 10 20 s may play a role in controlling the bubble wall type during periods without rip currents the location of the bubble wall is controlled by the incoming wave field simultaneous turbulence dissipation measurements 0 4 m above the seafloor show clear dependence on the local water depth beneath incoming waves the acoustical backscatter data are interpreted using in situ bubble and turbulence measurements in conjunction with a simple model based on bubble sorting by buoyancy dissolution and turbulence

unusually cu rich magmas associated with giant porphyry copper deposits evidence from bingham utah mass balance constraints indicate that formation of giant porphyry copper deposits pcds requires either highly efficient collection of cu from large volumes of magma or unusually cu rich parent magmas support for the second of these possibilities has been discovered in the form of mafic enclaves with abundant bornite and chalcopyrite in the last chance stock one of the parent intrusions of the giant bingham pcd utah united states mineral assemblages and compositions indicate that the last chance enclaves are autoliths consisting of phases that crystallized from the intrusion and that the intrusion was unusually enriched in cu one possible mechanism for generating cu rich magmas is fractional crystallization during pyrrhotite undersaturated conditions the high fo 2 conditions observed for the last chance stock may have allowed such an evolution alternatively if the magma has not undergone significant fractionation early crystallization of chalcopyrite and bornite from the magma would indicate that the lower crustal source region for the magma probably contained cu fe sulfides possible cu rich source regions are a subcrustal mafic intrusion with sulfide cumulates or a deeply buried metamorphic terrane containing cu deposits such as those in the curaca valley brazil or okiep south africa heterogeneous distribution of cu fe sulfides in an okiep type source terrane would produce local pcds such as bingham or large accumulations of cu fe sulfides possibly in the form of cumulates in subcrustal intrusions at convergent margins could produce giant pcd provinces such as those in indonesia papua new guinea and central chile

drifter measurements in a laboratory rip current 1 this paper investigates circulation in a laboratory rip current system using large numbers of lagrangian drifters with supplementary current meter and water level measurements these represent the most dense measurements to date of laboratory rip circulation over a large spatial area overall circulation is found to be very unsteady with strong changes in circulation apparent at many length and time scales drifter and current meter measurements are compared in the rip channel and stokes drift is found to be a significant component of drifter velocities in this region estimated generation of circulation is compared with computed bottom friction dissipation with good agreement the mean cellular circulation about a dividing streamline is found to be surprisingly small when compared with computed rates of generation of circulation finally the divergence of volume flux computed using drifters is found to be significant with depth varying wave induced mass transport depth varying eulerian velocities and velocity drifter concentration effects the likely sources of error

observations of nearshore circulation rip currents a sector scanning doppler sonar was deployed at the end of the scripps institution of oceanography pier aimed in toward the surf zone estimates of acoustic backscatter intensity and radial velocity were obtained seaward of the break point over a wedge with an arc of about 45 and a radius of 200 to 400 m the acoustic intensity is proportional to some combination of the bubble density and the suspended sediment in the water well defined jets of water extending seaward from the surf zone or rip currents were observed these rip currents occurred episodically recurred aperiodically one to four times per hour or so and lasted several minutes each the water transported offshore within the rips was rich in suspended sediment and bubbles producing distinctive bright patterns that can be easily recognized in successive images of backscatter intensity from the sonar fluid velocities were estimated from the doppler shift of the sonar signal approaching 0 7 m s in some of the events simultaneously a transect of temperature density and turbidity within the rip current was obtained with conductivity temperature depth ctd and optical backscatter strength obs sensors these data describe the ejection of warm turbid water from the surf zone and provide a comparison between the acoustic intensity and the optical turbidity of the fluid the horizontal extent of the sonar measurements and the vertical resolution of the ctd obs measurements complement each other in the study of the dynamics of the nearshore environment exchange rates are not fully resolved here since only one seaward jet is contained within the field of view however these observations suggest that rip currents could cause significant exchange between the nearshore and offshore waters

open ocean surface wave measurement using doppler sonar in october november 1983 doppler sonars mounted on the research platform flip were used to scatter 75 khz sound from the underside of the sea surface at low angle as well as from the interior of the mixed layer surface gravity waves were seen in velocity estimates from the surface scattering sonar even though the wave conditions were unusually calm valid measurements of sea surface motion were obtained over the range interval 600 to 1400 m from flip a second sonar which transmitted horizontally and scattered from the interior of the mixed layer also sensed surface waves although with amplitude reduced in proportion to the decay of the motions with depth wave number frequency spectra of the observed motions are consistent with linear theory the existence emergence of this technology enables the synthesis of kilometer long surface wave arrays in the open sea without the cost and logistical support usually associated with large aperture arrays in addition the doppler acoustic approach can provide information on lower frequency surface currents and on the spatial variations in these low frequency currents such as langmuir cells which might affect wave propagation

acoustic attenuation in very shallow water due to the presence of bubbles in rip currents an experiment was performed just off the research pier at the scripps institute of oceanography to determine the acoustic effects of small bubbles in very shallow water 6 m depth the distance offshore was 300 m the propagation lengths were 2 10 m and the frequency range was from 39 to 244 khz during the experiment rip currents passed through the field of measurement instruments these rip currents were laden with bubbles created in the surf between the instruments and the shore the effects of these rip currents on the spatial distributions of the resulting acoustic attenuation are discussed from the attenuation data the bubble distributions are calculated using a new iterative approach caruthers et al in press j acoust soc am that is based on the well known resonant bubble approximation calculated bubble distributions varied from an essentially uniform lack of bubbles during quiescent periods to highly inhomogeneous and dense bubbly regions within rip events such observed distributions were consistent with measurements made by other investigators during the experiment

bubble transport in rip currents a number of remote and in situ acoustical sensors were mounted in the surf zone off scripps pier la jolla california during march 1997 and used to characterize rip currents and their ability to transport bubbles offshore from the surf zone the bubble size distributions and air fractions at the injection point were measured using an acoustical resonator and a conductivity sensor right in the surf zone the offshore moving bubble plume was tracked with a multibeam 100 khz doppler sidescan sonar giving the spatial extent and offshore variability in the rip events as well as information about the surface wave field furthermore three acoustical resonators were mounted at 2 5 m depth 55 60 m farther offshore to probe the bubble field 300 400 s after injection these results are interpreted using models that include bubble buoyancy and dissolution rip current advection and the turbulent boundary layer which is represented by the christoffersen and jonsson 1985 formulation

copper solubility in a basaltic melt and sulfide liquid silicate melt partition coefficients of cu and fe the solubility of copper in a sulfur saturated basaltic melt has been determined at 1245 c as a function of fo2 and fs2 copper solubilities at log fo2 values between 8 and 11 fall into two distinct populations as a function of fs2 at log fs2 values 1 65 sulfide liquid that coexists with the basaltic glass quenches to sulfur poor bornite solid solution at log fs2 values in excess of 1 65 the sulfide liquid quenches to a complex intergrowth of sulfur rich bornite and intermediate solid solution copper solubilities in the low fs2 population range from 594 to 1550 ppm whereas those in the high fs2 population range from 80 to 768 ppm sulfide liquid silicate liquid partition coefficients d for cu and fe range from 480 to 1303 and 0 7 to 13 6 respectively metal sulfur complexing in the silicate liquid is shown to be insignificant relative to metal oxide complexing for fe but permissible for cu at high fs2 values on log dfe sulfide silicate and log dcu sulfide silicate vs log fs2 log fo2 diagrams both fs2 populations show distinct but parallel trends the observation of two d values for any fs2 fo2 ratio indicates nonideal mixing of species involved in the exchange reaction the two distinct trends observed for both cu and fe are thought to be due to variations in activity coefficient ratios e g feo fes and cuo0 5 cus0 5 results of the experiments suggest that accurate assessments of fs2 fo2 ratios are required for the successful numerical modeling of processes such as the partial melting of sulfide bearing mantle and the crystallization of sulfide bearing magmas as well as the interpretation of sulfide mineralogical zoning in addition the experiments provide evidence for oxide or oxy sulfide complexing for cu in silicate magmas and suggest that the introduction of externally derived sulfur to mafic magma may be an important process for the formation of cu rich disseminated magmatic sulfide ore deposits

major to trace element analysis of melt inclusions by laser ablation icp ms methods of quantification current techniques for the quantification of melt inclusion chemistry require that inclusions are compositionally homogeneous and that post entrapment devitrification or crystallization onto the inclusion walls could be reversed by appropriate re melting laser ablation icp ms provides a technique by which single heterogeneous inclusions can be analysed thus avoiding the above prerequisites because host mineral is ablated with the inclusion quantification of the melt composition necessitates deconvolution of the mixed signal by an internal standard this can be obtained in various ways including 1 a fixed pre determined concentration of a given element in the melt 2 whole rock differentiation trends in a given igneous suite 3 a constant measured distribution coefficient between the host and the inclusion melt and 4 determination of the volume ratios between the inclusion and total ablated volume these four approaches were tested on a large set of cogenetic inclusions from a single plagioclase crystal in a rhyodacitic intrusion results suggest that quantification through whole rock differentiation trends is the most widely applicable the most accurate and the least time consuming technique provided that the resulting data are critically interpreted with regard to the underlying assumptions uncertainties on the calculated element concentrations in the inclusions depend on the mass ratio between the melt inclusion and the host for a given ablation they are of the order of 10 if the melt inclusion contributes more than 20 to the bulk analytical signal of a particular element calculated limits of detection for spherical 10 m melt inclusions are of the order of a few ppm for elements strongly enriched in the melt relative to the host crystal concentrations in the melt inclusions can be determined even for elements enriched in the host mineral but in this case uncertainties and calculated limits of detection increase with the concentration in the host the uncertainty on the melt composition from a set of cogenetic inclusions can be commonly decreased by calculating of an uncertainty weighted average of the concentration and their uncertainty

a model for the horizontal directionality of breaking wave noise in the surf zone a model is presented for the horizontal directionality of the noise generated by individual breaking waves in the surf zone the model is based on the interaction between sound radiated by ringing bubbles created in a breaking wave crest and the population of acoustically quiescent bubbles left on the seaward side of the wave in the shallow water waveguide the effect of the quiescent bubbles is to absorb sound from all but the very ends of the breaking crest resulting in the formation of acoustic hot spots the model calculations are in good agreement with observations of the horizontal directionality of noise from individual breaking waves in the surf zone

application of proton microprobe data to trace element partitioning in volcanic rocks abstract in situ proton microprobe analyses are used to calculate partition coefficients d for mn fe cu zr ga rb sr y zr ba and pb and more restricted data for ni ge nb and as in pyroxenes olivines biotites hornblendes feldspars and fe ti oxides from 32 volcanic rocks all with glassy matrices these range from leucitite and picritic basalt to high silica and peralkaline rhyolites data for pigeonite aenigmatite allanite and leucite are included where these occur as additional phases coefficients have also been rayleigh fractionation corrected this correction being significant for those elements with high coefficients in specific mineral phases and where pronounced crystallisation has occurred partition coefficients are presented as plots vs nbo t ratios of coexisting glasses melts negative correlations are observed based on log transformed data for mn zn fe and y pyroxenes mn zn and fe olivines mn and zn fe ti oxides nb y sr and zr hornblendes sr plagioclase and ba cu zn and fe feldspars these element partition coefficients are not correlated with bulk mineral compositions zr and ga are not correlated with either glass or mineral compositions except zr in hornblende the correlations support the role of melt polymerisation in controlling element partitioning at least for those elements listed although possible effects of temperature cannot be uniquely isolated in the present data set the coefficients presented here are generally consistent with published values for equivalent rock compositions one difference being that some of the higher published coefficients e g sr in plagioclase are not matched in the present data set from a practical viewpoint the relative regularity of the coefficient data presented does facilitate choice of relevant coefficient values that are required for petrogenetic modelling procedures

copper partitioning between felsic melt and h2o co2 bearing saline fluids abstract analysis of fluid inclusions from porphyry copper deposits reveals that magmatic vapor and brine are vital for the removal of copper from arc magmas and its transport to the site of ore deposition experiments in melt vapor brine systems allow for investigation of the partitioning of copper between silicate melts and volatile phases at magmatic conditions the presence of co2 affects both the pressure at which a melt saturates with respect to volatile phases therefore the partitioning of copper among felsic rhyolitic melt vapor and brine in co2 bearing experiments was examined to provide insights into copper partitioning and the generation of porphyry copper and related deposits we present results from experiments performed at 800 c and 100 mpa in co2 bearing melt vapor brine systems with x co 2 v b 0 10 and 0 38 the compositions of vapor and brine inclusions and run product glasses were determined during the course of this investigation microthermometric measurements of fluid inclusions show an increase in the salinity of the magmatic brine 65 to 70 wt nacleq and decrease in the salinity of the vapor 3 5 to 1 wt nacleq as x co 2 is increased from 0 10 to 0 38 the partitioning of copper between brine and vapor d cu b v 2 increases from 25 6 at x co 2 0 10 to 100 30 at x co 2 0 38 the partitioning of copper between vapor and melt d cu v m 2 decreases from 9 6 3 3 at x co 2 0 10 to 2 0 8 at x co 2 0 38 these data demonstrate that copper partitioning in sulfur free co2 bearing systems is controlled by the changes in the salinity of the vapor and brine that in turn are functions of x co 2 no change in the apparent equilibrium constants for cu na exchange was observed in fe bearing experiments which supports a salinity dependent model for copper partitioning an existing model mvpart for ore metal partitioning between melt and volatile phases was modified to incorporate partitioning data from co2 bearing experiments the model can be used to predict trends in efficiency of removal of copper from melts into exsolving co2 bearing magmatic volatile phases at a fixed pressure and temperature the co2 mvpart model predicts that co2 rich x co 2 0 38 magmatic vapor will remove half of the available copper from the melt without a contribution from the brine compared to low co2 x co 2 0 10 systems thus periods of co2 rich vapor exsolution are not expected to be associated with efficient removal of copper from shallow felsic melts

contribution of mafic melt to porphyry copper mineralization evidence from mount pinatubo philippines and bingham canyon utah usa mount pinatubo in the philippines known for its cataclysmic eruption in 1991 hosts several porphyry copper deposits and active geothermal systems an underlying mafic melt supplied much of the sulphur for the dacitic magma and its injection into the dacitic magma chamber triggered the eruption the eruption caused purging of the sulphur rich fluid from the dacite to the atmosphere and extensive fracturing similar events took place at bingham canyon utah site of the largest copper and gold deposit in north america at 38 ma the bingham canyon mineralization took place beneath an active stratovolcano and pyroclastic flows contemporaneous with the mineralization show evidence for magma mingling ascent of mafic melt supplied sulphur and chalcophile elements to the felsic magma which consolidated to form the bingham stock and its underlying magma chamber injections of the mafic melt caused periodic eruptions of felsic magma to form the stratovolcano and deposition of sulphide minerals in highly fractured rocks in and around the stock

infragravity rip current pulsations 1 the origins of rip current pulsations within the infragravity frequency band 0 004 0 04 hz are determined from measurements made with arrays of colocated pressure and velocity sensors deployed on a beach with persistent rip current channels the observations indicate significant energy in cross shore infragravity velocities that varies spatially in the alongshore due to the presence of rip channels infragravity velocities are smaller within the rip channel than on the shore connected shoal owing to differences in water depth rip current pulsations at infragravity frequencies are linked to standing infragravity motions but not to the ponding and subsequent release of water by wave group pumping

giant ore deposits formed by optimal alignments and combinations of geological processes giant ore deposits are priority targets for mining companies a review of the characteristics of several giant porphyry and epithermal deposits worldwide suggests that they formed from ordinary processes that were fortuitously operating at maximum efficiency

fractional crystallization of primitive hydrous arc magmas an experimental study at 0 7 gpa differentiation of mantle derived hydrous basaltic magmas is a fundamental process to produce evolved intermediate to sio2 rich magmas that form the bulk of the middle to shallow continental and island arc crust this study reports the results of fractional crystallization experiments conducted in a piston cylinder apparatus at 0 7 gpa for hydrous calc alkaline to arc tholeiitic magmas fractional crystallization was approached by synthesis of starting materials representing the liquid composition of the previous higher temperature experiment temperatures ranged from near liquidus at 1 170 c to near solidus conditions at 700 c h2o contents varied from 3 0 to more than 10 wt the liquid line of descent covers the entire compositional range from olivine tholeiite 1 170 c to high silica rhyolite 700 c and evolves from metaluminous to peraluminous compositions the following crystallization sequence has been established olivine clinopyroxene plagioclase spinel orthopyroxene amphibole titanomagnetite apatite quartz biotite anorthite rich plagioclase and spinel are responsible for a marked increase in sio2 content from 51 to 53 wt at 1 040 c at lower temperatures fractionation of amphibole plagioclase and fe ti oxide over a temperature interval of 280 c drives the sio2 content continuously from 53 to 78 wt largest crystallization steps were recorded around 1 040 c and at 700 c about 40 of ultramafic plutonic rocks have to crystallize to generate basaltic andesitic liquids and an additional 40 of amphibole gabbroic cumulate to produce granitic melts andesitic liquids with a liquidus temperature of 1 010 c only crystallize 50 over an 280 c wide range to 730 c implying that such liquids form mobile crystal mushes 50 crystals in long lived magmatic systems in the middle crust allowing for extensive fractionation assimilation and hybridization with periodic replenishment of more mafic magmas from deeper magma reservoirs

analysis of surf zone turbulence measurements of turbulent kinetic energy k under surf zone waves are analyzed to show how k varies over depth between breaker point and shoreline and how k depends on the beach slope it is found that the variation of k over depth is remarkably weak large values being measured a few percent of the depth above the bottom a simple model for the dissipation mechanism makes it possible to derive an empirical formula for the time averaged k that accurately describes all the data considered reliable

air entrainment processes and bubble size distributions in the surf zone abstract a new optical instrument was deployed in the surf zone in a trial experiment to measure bubble size distributions and visualize air entrainment and bubble formation mechanisms within breaking surf images of bubbles and the evolving air water mixture inside and beneath breaking wave crests are presented the images resolve features of the air water mixture to length scales of hundreds of microns across a 3 7 cm field of view two qualitatively different large scale air entrainment processes are observed first intrusions of air and water thought to be created by jets penetrating the water s surface fragment into plumes of bubbles second an air cavity trapped by the overturning wave crest is observed to disintegrate into bubbles the timescale for the evolution from a compacted air water mass to individual bubbles was on the order of 90 ms or less for both of these processes in addition small scale air filaments hundreds of microns wide and millimeters long have been discovered beneath wave

copper partitioning between silicate melts and amphibole experimental insight into magma evolution leading to porphyry copper ore formation abstract a series of piston cylinder experiments were conducted to determine the partition coefficient of cu between amphibole and andesitic to rhyolitic silicate melts the experiments were run at t 740 990 c p 0 7 gpa oxygen fugacity f o 2 ranging from that of the ni nio buffer nno to 2 3 log units higher nno 2 3 and dissolved water in variable concentrations under saturated to saturated conditions fixed metal activities were imposed by using au 97 cu 3 and au 92 cu 8 alloy capsules which allowed simultaneously determination of cu solubility our data demonstrate that cu solubilities in both the silicate melt and amphibole decrease with decreasing temperature the solubility of cu decreases by a factor of 6 from 990 to 740 c in equilibrium with andesitic to rhyolitic melt compositions the average amphibole silicate melt partition coefficient of cu d cu amph melt is 0 066 0 006 and is essentially constant without showing any correlation with silicate melt composition dissolved water concentration temperature or f o 2 the low d cu amph melt value suggests that amphibole crystallizing at any stage of calc alkaline magma evolution is unable to scavenge a significant fraction of the initially available cu from the melt however d cu amph melt is high enough to yield precisely measurable cu concentrations in natural amphiboles as d cu amph melt remains constant along the liquid line of descent of calc alkaline magmas amphibole compositions may thus be used as a proxy to monitor the evolution of the cu concentration in the silicate melt not the bulk magma if sulfide is present this may be useful for understanding the metallogenic evolution of intrusive rocks in which silicate melt inclusions in minerals are generally absent as most porphyry type cu ore deposits are associated with upper crustal intrusions in situ microanalysis of inclusion free amphiboles in such rocks may help understand ore genesis and might also be used in mineral exploration to assess the fertility of prospective magmatic systems

magmatic sulfides and au cu ratios in porphyry deposits an experimental study of copper and gold partitioning at 850 c 100 mpa in a haplogranitic melt pyrrhotite intermediate solid solution gold metal assemblage at gas saturation abstract the behavior of copper and gold in the phase assemblage pyrrhotite po intermediate solid solution iss haplogranitic melt gold metal capsule at 850 c 100 mpa and gas saturation ah2o 0 9 has been investigated the results are presented as nernst partition coefficients the partition coefficient dcupo melt 2 6 0 3 103 1 was determined for po and melt in equilibrium with an iss of composition cu 19 1 fe 30 1 s 51 1 2 for gold the partition coefficients are dauiss melt 5 7 2 2 103 1 between iss and melt and daupo melt 140 40 1 between po and melt these imply dauiss po 42 9 1 between iss and po the oxygen fugacity for the experiments log f o 2 13 2 0 3 1 was determined by using the hydrogen sensor technique the sulfur fugacity log f s 2 1 0 0 7 1 was calculated from the composition of po in our experiments melts at iss saturation have cu fe by weight of ca 1 100 the results indicate that crystallization of iss may deplete a melt in gold and crystallization of po may deplete a melt in copper however a melt saturated with iss at a given bulk composition temperature pressure oxygen and sulfur fugacity and feo concentration will have a fixed concentration of cu preventing strong depletion of the melt in cu until iss is fractionated from the melt or changes in environmental conditions destabilize iss a thermodynamic model for the partitioning of cu and au between po and melt in terms of oxygen and sulfur fugacity indicates that dcupo melt and daupo melt may increase greatly with increasing sulfur fugacity and decreasing oxygen fugacity within the po stability field the model also suggests that destabilization of both iss and po relative to magnetite due to changes in oxygen and sulfur fugacities can result in the release of cu and au from the sulfides to the melt

petrogenesis of oceanic plagiogranites by partial melting of gabbros an experimental study we performed hydrous partial melting experiments at shallow pressures 0 2 gpa under slightly oxidizing conditions nno oxygen buffer on oceanic cumulate gabbros drilled by odp ocean drilling program cruises to evaluate whether the partial melting of oceanic gabbro can generate sio2 rich melts with compositions typical of oceanic plagiogranites the experimental melts of the low temperature runs broadly overlap those of natural plagiogranites at 940 c the normalized sio2 contents of the experimental melts of all systems range between 60 and 61 wt and at 900 c between 63 and 68 wt these liquids are characterized by low tio2 and feotot contents similar to those of natural plagiogranites from the plutonic section of the oceanic crust but in contrast to fe and ti rich low temperature experimental melts obtained in morb systems at 950 c the 1 500 m long drilled gabbroic section of odp hole 735b legs 118 and 176 at the southwest indian ridge contains numerous small plagiogranitic veins often associated with zones which are characterized by high temperature shearing the compositions of the experimental melts obtained at low temperatures match those of the natural plagiogranitic veins while the compositions of the crystals of low temperature runs correspond to those of minerals from high temperature microscopic veins occurring in the gabbroic section of the hole 735b this suggests that the observed plagiogranitic veins are products of a partial melting process triggered by a water rich fluid phase if the temperature estimations for high temperature shear zones are correct up to 1 000 c and a water rich fluid phase is present the formation of plagiogranites by partial melting of gabbros is probably a widespread phenomenon in the genesis of the ocean crust

longshore current and wave height modulation at tidal frequency inside the surf zone data were acquired continuously during the 19 day delilah nearshore experiment with a specific objective of examining variability of the longshore current at tidal frequencies it is hypothesized that breaking wave heights inside the surf zone are strong functions of the depth which are modulated by the tidal variations and since radiation stress is a function of the wave height longshore currents are forced at the tidal frequency inside the surf zone the measured longshore current variations at tidal frequency are the same order of magnitude as the mean longshore current variations for moderate wave height conditions indicating that the tide is a dominant mechanism associated with longshore current variability simulations of the magnitude and phase of the longshore current variability with tide elevation using the model by thornton and guza 1986 are used to explain observations the measured tidal elevation and longshore current are in phase in the inner surf zone and out of phase in the outer surf zone as predicted by the model verifying the hypothesis

laser ablation icp ms analysis of silicate and sulfide melt inclusions in an andesitic complex i analytical approach and data evaluation quantitative microanalysis of entire silicate and sulfide melt inclusions by excimer laser ablation inductively coupled plasma mass spectrometry la icpms has been applied to extrusive and shallow intrusive rocks from the andesitic farallon negro volcanic complex northwestern argentina silicate melts are trapped in pyroxene amphibole plagioclase and quartz and sulfide melts are trapped in amphibole details of the analytical approach and the quantification procedure are given and the results are evaluated to test the accuracy of the technique and the validity of the interpretation of analytical signals similar compositions of silicate melt inclusions trapped in truly co precipitating minerals show that the quantification approach of melt inclusion compositions from la icpms signals through an internal standard is valid this correspondence also shows that melt inclusions investigated in this study are not significantly influenced by the boundary layer around a growing crystal or by post entrapment modifications post entrapment diffusive re equilibration only affected the fe and mg content of melt inclusions in mafic phases thus melt inclusions are representative samples of the melt from which the host mineral crystallized with regard to most major and trace elements sulfide melt inclusions present as pyrrhotite with exsolution of au and cu in phases separated during cooling were analyzed for their bulk fe cu and au content and the abundance of these elements was quantified using a silicate glass as external standard the validity of this calibration was tested by comparing electron microprobe analyses of fe cu ni and co in homogeneous sulfide minerals with la icpms results identical results within calculated uncertainty one standard deviation of five to nine analyses mostly between 1 and 5 wt rsd demonstrate that for these elements measured element ratios are independent of the matrix using our analytical setup

the magnetite crisis in the evolution of arc related magmas and the initial concentration of au ag and cu the association of large au cu ag ore deposits with convergent margins is commonly attributed to the higher content of chalcophile elements in the parental magmas generated at subduction zones compared with mid ocean ridges we present new geochemical data for arc like relatively oxidized mantle derived basalt to rhyolite magmas from the pual ridge and vicinity eastern manus basin which show that the initial abundances of base and precious metals in the parental basalts are similar to those of mid ocean ridge basalt morb the contents of au cu and ag are built up in the evolving pual ridge liquids to levels considerably in excess of those in morb because unlike morb they are not saturated in a sulfide phase which is a consequence of their being more oxidized than morb the behaviour of s during the evolution of the pual ridge magmas is obscured by late stage so2 loss during eruption but we show that it may be inferred by using se as a proxy because this element follows s closely during magmatic evolution except it is not lost during low pressure near sea floor degassing the onset of magnetite fractionation at 60 wt sio2 and an mg number of 40 is accompanied by an abrupt decrease in the contents of au cu and ag previously attributed to separation of cu au rich fluid which is also shown by se implying that magnetite fractionation triggers sulfide saturation petrological modelling reveals that the amount of magnetite fractionation involved is sufficient to convert most of the s originally dissolved in the magma as sulfate so42 to sulfide s2 triggering saturation in a cu rich sulfide phase tentatively identified as bornite cu5fes4 this sulfide phase sequesters au and ag elements with the same valence as cu in sulfides but not other potentially chalcophile elements such as ni re and pt which suggests that the phase is crystalline rather than an immiscible sulfide melt the relatively high contents of cu and au characteristic of evolved convergent margin magmas requires no enrichment from subducted material instead the association of major cu au deposits with convergent margin magmatism results specifically from the process of magmatic evolution under oxidizing conditions this same property also leads to early magnetite fractionation triggering the abrupt saturation in the cu rich sulfide hence the easily recognizable trend of magmatic evolution under oxidizing conditions i e the sharp drop in chalcophile element concentrations may be an exploration guide to economic au ag cu provinces or a crucial pre enrichment step in the formation of such deposits the decrease in p2o5 and sr at the same stage in the fractionation sequence 60 wt sio2 indicates that saturation in apatite is concomitant with magnetite sulfide saturation in the eastern manus basin

nearshore circulation over transverse bar and rip morphology with oblique wave forcing there is a paucity of field data to describe the transition in nearshore circulation between alongshore meandering and rip current systems a combination of in situ current meters and surf zone drifters are used to characterize the nearshore circulation over a transverse bar and rip morphology at pensacola beach florida in the presence of relatively low energy oblique waves current speeds vary in response to the relative wave height ratio hs h which defines the degree and extent of breaking over the shoal in the absence of wave breaking the nearshore circulation was dominated by an alongshore current driven by the oblique waves as waves begin to break across the shoal 0 2 0 5 the meandering current is replaced by an unsteady rip circulation that moves offshore between the shoals before turning alongshore in the direction of wave advance outside the surf zone the increase in wave dissipation is associated with an increase in very low frequency vlf variations in the current speed across the shoal and in the rip channel that caused the circulation to oscillate between an offshore and an alongshore flow the unsteady nature of the nearshore circulation is responsible for 55 of all surf zone exits under these more dissipative conditions in contrast only 29 of the drifters released from the shoal exited the surf zone and bypassed the adjacent shoal with the alongshore meandering current while the currents had a low velocity maximum of 0 4 m s 1 and would not pose a significant hazard to the average swimmer the results of this study suggest that the transverse bar and rip morphology is sufficient to create an alongshore variation in wave dissipation that forces alongshore meandering and low energy rip circulation systems under oblique wave forcing copyright 2013 john wiley sons ltd

surf zone eddies coupled with rip current morphology 1 energetic very low frequency vlf frequencies 0 004 hz surf zone eddies szes were observed on a beach composed of shore connected shoals with quasi periodic 125 m incised rip channels at sand city monterey bay california incident waves consisted of predominantly shore normal narrow banded swell waves szes were located outside the gravity region in alongshore wave number ky spaced within the vlf band and did not appear to exist in higher frequency bands the szes were significant urms vlf 0 25 m s and constant in intensity within the surf zone shore connected shoals and rip channels and rapidly decreased offshore the alongshore and cross shore sze velocity variances were similar in magnitude vlf sze velocities were not forced by vlf surface elevations and were not well correlated with rip current flows r2 0 18 there is an indication that the szes were related to wave forcing with the szes statistically correlated with incoming sea swell wave height r2 0 49 f ky spectral estimates illustrate a strong relationship between rip channel spacing and sze cross shore velocities ky 0 008 m 1 and minimal sze alongshore velocity variation ky 0 m 1 data analysis suggests that the szes are not simply instabilities of an unstable rip current jet a simple conceptual model suggests that sze f ky spectra can be explained by the entire rip current circulation cells oscillating predominantly in the cross shore and slightly in the alongshore

mean lagrangian flow behavior on an open coast rip channeled beach a new perspective article i nfo the accepted view of rip currents is that they are an efficient mechanism for transporting material out of the surf zone previous rip current campaigns on natural beaches have focused on eulerian measurements with sparse in situ pressure and current meter arrays here for the first time spatially synoptic estimates of rip current flow patterns vorticity and lagrangian transport behavior are measured in the field using a fleet of 30 position tracking surfzone drifters during multiple rip current occurrences on an open coast beach in monterey ca contrary to the classic view shepard et al 1941 the rip current flow field consisted of semi enclosed large scale vortices that retained the drifters and resulted in a high number of lagrangian observations that are temporally and spatially repeated approximately 19 of the drifters deployed in the rip currents exited the surf zone per hour on average during the experiments the observed surf zone retention of drifters is consistent with measurements from different open coast beach rip current systems 14 at meso macrotidal truc vert france and 16 at macrotidal perranporth united kingdom the three hour average cross shore rip current velocity at monterey was 30 cm s with peak time averaged velocities of 40 60 cm s depending on wave and tidal conditions drifters that episodically exited the surf zone were transported approximately 2 surf zone widths offshore at 20 cm s published by elsevier b v

geochemistry of the volcanic island of annobon gulf of guinea abstract annobon island in the gulf of guinea is composed predominantly of volcanic rocks of alkali character ranging from basanites to trachytes the most primitive rocks basanites were probably formed by variable degrees of melting of a single upper mantle source previously enriched in incompatible trace elements the more differentiated rocks could have been derived from basanitic magma by fractional crystallization mainly involving kaersutite clinopyroxene and plagioclase it seems that overall there are no obvious differences in alkali basalt sequences from oceanic and continental environments

solubility of copper in a sulfur free mafic melt the solubility of cu in s free mafic melts has been measured at a series of o2 values and temperatures of 1245 and 1300 c at constant temperature cu solubility increases from 0 04 wt at log o2 11 9 to 1 10 wt at log o2 7 4 copper solubilities were in excess of 8 wt in two runs controlled at very high o2 conditions of 10 1 4 and 10 22 partitioning of cu between metal and glass shows a strong o2 dependence with dcumetgl ranging from 90 at log o2 7 4 to 2190 at log o2 11 9 slopes of cu solubility and dcumet gl vs log o2 suggest that cu dissolves predominantly in the 1 valence state copper solubility decreases with increasing temperature at constant o2 similar to experimental results for ni co and mo dingwell et al 1994 holzheid et al 1994 the data are consistent with cu dissolution as an oxide represented by cuo0 5 and suggest that changes in o2 fe2 fe3 variations and cu1 complexation with fe3 may have large effects on the distribution of cu between silicate and sulfide magmas results also suggest that the extraction of oxide bonded cu in mafic magmas by externally derived s may be an important mechanism in the generation of cu rich sulfide ores

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

mean currents and sediment transport in a rip channel measurements of hydrodynamics and suspended sediment transport were carried out along a cross shore transect in a rip channel a tidally induced threshold for rip flow initiation was found this threshold depended upon the degree of wave energy dissipation and could be identified through a critical value of the ratio of significant wave height to water depth s in the rip neck with normally incident waves rip current velocities were well correlated with velocities predicted from a simple model involving the onshore mass transport in asymmetric breaking waves crossing the bar hydrodynamics and sediment transport were tidally modulated with strong offshore directed rip currents and associated offshore sediment transport due to the mean flow at low tide at high tide when the rip was inactive the tendency was for weak onshore directed mean flows and or oscillatory incident waves transporting smaller amounts of sediment landward the net result was a gradual lowering of the topographic relief along the rip channel with net deposition seaward of the rip outside the surf zone transport was mainly landward due to oscillatory incident waves

triggers for the formation of porphyry ore deposits in magmatic arcs porphyry ore deposits supply much of the copper molybdenum gold and silver used by humans a review of the main processes that trigger porphyry ore formation suggests that sulphide saturation of the magmas that supply the metals could be the overriding mechanism that helps control the temporal and spatial distribution of the ore deposits

can economic porphyry copper mineralization be generated by a typical calc alkaline melt numerical simulation of chlorine and copper partitioning between a crystallizing melt and exsolving aqueous fluids indicates that typical calc alkaline magmas contain sufficient copper chlorine and water to produce economic porphyry copper mineralization neither an elevated copper content in the magma nor an additional large volume of magma are required to provide metals or volatiles the most important variables that determine the volume of melt necessary to produce sufficient copper are the degree of compatible behavior displayed by copper the ratio of initial water in the melt to the water saturation level and the initial chlorine water ratio of the melt the absolute values for initial water in the melt and water content at saturation are relatively unimportant in determining the required melt volume the bulk salinity of the exsolved fluid may vary from 2 0 wt nacl to saturation levels 84 wt nacl at 700 c indicating that boiling is not necessary to produce high salinity brines at appropriate p t xnacl conditions the magmatic aqueous fluid separates into a saline liquid which transports most of the copper and a low salinity vapor the salinities of the two immiscible phases are governed by the p t conditions while the bulk fluid salinity determines the mass fractions of liquid and vapor formed pressure quenching causes rapid crystallization of the aplitic groundmass in porphyritic rocks associated with copper mineralization and significantly reduces the amount of chlorine and copper partitioning to the aqueous fluid this results in abrupt and possibly large reductions in fluid salinity and causes copper to become concentrated in the melt as copper is transported from the melt by the earliest exsolving fluids in deep 2 0 kbar systems and by late exsolving fluids in shallow 0 5 kbar systems the relative timing of pressure quenching aplite formation and fluid transport of copper from the melt can vary significantly in systems produced under different confining pressures model results incorporating petrologic constraints determined for yerington nevada are in good agreement with observed mineralization