turbulence measurements over a sand wave in lower chesapeake bay virginia u s a abstract measurements of turbulent shear stress 5 cm above a sediment bed are described for five stations distributed along a transverse profile of an estuarine sand wave in lower chesapeake bay virginia u s a time series analyses of the velocity data reveal three kinds of constituents 1 components of long period 2 wind wave components and 3 turbulence the energy in the turbulent part of the records is highly attenuated in comparison with that of the low frequency components furthermore at all except the lowermost frequencies the energy contained in the horizontal component of the flow is less than that contained in the vertical component the excess energy at the low frequency part of the spectrum as compared to the high frequency part is explained by 1 the input of energy from wind waves 2 damping of turbulence or 3 both causes the first evidently is the main cause suspended sediments and stable density stratification reduce turbulence but they act mainly on the vertical component a schematic model presented here indicates that oscillating flow over a rugose bed induces additional fluctuations in the vertical component estimates of reynolds shear stress are small and most are negative time series plots of the reynolds stress show 1 small spikes in all records in which the instantaneous shear stresses are very close to zero and 2 intermittent large spikes in most instances within a spike the fluctuating horizontal component of the turbulent velocity u and the vertical counterpart w are of the same sign and w u these results are in agreement with the proposed model of flow over rippled surfaces the findings and concepts developed in the study indicate that even though a flow over the bed actually produces a significant boundary shear stress it cannot be properly measured very close to the bottom based on the reynolds stress idea when making nearbed measurements in turbulent flows in open waters with tidal currents surface waves stable density structures a rugose bed and with sediment in suspension one may encounter a reduction in turbulence and a degradation of the usual correlation between u and w under these conditions the profile method for determining the shear stress using mean flow values may be more reliable

application of thermochronology to hydrothermal ore deposits thermochronology finds many applications in economic geology utilizing temperature sensitive radiometric dating techniques to reveal low temperature upper crustal processes can elucidate many aspects of deposit genesis including timing and duration of mineralization processes rate of exhumation and erosion of intrusive ore deposits and comparative preservation potential the tools are utilized to best advantage when combined with other thermochronometry techniques that provide complementary information in addition when thermochronometers are combined with geochronometers e g zircon u pb over 800 c of thermal history is revealed from emplacement to erosion fig 1 with the advent of computational algorithms that provide more accurate and detailed models of thermochronology results the economic geologist has a powerful tool to use when assessing economic favorability of a region or prospect this chapter summarizes the various ways that low temperature thermochronometers have been utilized in studies of economic mineralization and primarily focuses on studies of porphyry ore deposits these deposits are well characterized and provide a good platform from which to demonstrate the extended understanding of ore formation processes that is provided by thermochronology studies in this section we review the fundamental application of u th he fission track and 40ar 39ar thermochronometry methods to mineralized systems we then present a synopsis of how these techniques can be used in thermal history analysis either alone or in combination with other chronometers in order to provide more information on deposit genesis the discussion is presented from low through to higher temperature thermochronometers corresponding to their presentation on figure 1 u th he thermochronology as documented earlier in the volume u th he thermochronology is based on measuring the accumulation of radiogenic 4he produced from u and th decay the daughter helium is retained until the mineral is heated to a temperature at which its structure and helium retentivity change this closure temperature varies from

does flow variance affect bedload flux when the bed is dominated by grain roughness abstract previous studies have shown that spatial variance in fluid and critical shear stress caused by form roughness can increase bedload flux others have revealed that variance in flow velocity increases with relative submergence and that bed mobility is reduced at lower submergences the paper explores the link between these observations and addresses the following questions is grain roughness sufficient to cause variance in fluid shear stress and an increase in bedload flux if this variance changes with submergence does this mean that the increase is dependent on submergence and does this explain the change in mobility with submergence a simple statistical bedload model based on spatial distributions of fluid and critical shear stress has been used to explore these effects over a water worked gravel deposit estimates of spatially distributed fluid shear stress were gained from laboratory flume measurements of near bed flow velocity and a distribution of critical shear stress was simulated using a discrete particle model of the sediment distribution used in the flume the velocity data were used to describe the change in the spatial distribution of near bed velocity with relative submergence which allowed the effects of submergence on flux to also be considered the main conclusions were i spatial variance in fluid shear stress from grain roughness was not sufficient to have an appreciable effect on bedload flux over water worked gravel beds with a spatial distribution of critical shear stress ii spatial variance in critical shear stress caused by grain roughness had a much larger influence and increased bedload flux this was a similar level of increase observed in studies for conditions where form roughness was high iii spatially averaged estimates of fluid and critical shear stress should not be used to estimate bedload flux even if form roughness is low and iv a rise in relative submergence increased bedload flux this was due to changes in the spatial distribution of near bed velocity and not due to a lowering in the local flow velocity as has been suggested by previous studies

the geochemistry of rhenium and osmium in recent sediments from the black sea abstract the os isotopic composition of recent sediments from the black sea are reported with the concentrations of re os and major and minor elements osmium concentrations range from 0 23 to 0 69 ppb and re concentrations range from 21 to 85 ppb concentrations of both elements are large relative to average crustal material and are positively correlated with organic carbon 187 os 186 os ratios range from 5 7 to 7 1 all of these values are less radiogenic than the estimated 187 os 186 os ratio of seawater and average continental crust material variations in the os isotopic composition of these sediments are attributed to mixing of a hydrogenous component 187 os 186 os ratio between 7 and 9 and a less radiogenic detrital component 187 os 186 os ratio between 1 and 4 a mixing model is used to determine the fraction of os in the sediment associated with each component and the burial fluxes of re and os in the black sea are calculated in addition the data are used to estimate the magnitude of systematic error which such initial os isotopic heterogeneity may introduce into re os age determinations of ancient organic rich sediments

on the necessity of applying a rotation to instantaneous velocity measurements in river flows in studies on river channel flow turbulence it is often the case that the measured mean vertical velocity is different from zero indicating that the frame of reference of the current meter is not parallel to the flow streamline this situation affects the estimate of reynolds shear stress in the streamwise and vertical planes and consequently the analysis of the flow turbulent structure one way to solve this problem is to correct data by applying a rotation and this is reviewed in the first part of the paper however in fluvial geomorphology the studied flow is often complex and streamlines may exhibit significant changes from one point of measurement to the other in this context applying a rotation complicates the situation more than it simplifies it the second part of this paper examines the question of velocity data correction in complex flows using a field example of the turbulent boundary layer over a very rough gravel bed and a laboratory example taken from flow at a river channel confluence in both cases velocity vectors are spatially variable in the first case errors in the reynolds shear stress estimates are relatively low ranging from 13 to 7 per cent deg while in the second case they are much larger 200 to 164 per cent deg the significance of these errors on the interpretation of turbulence statistics in river channel flows is discussed we propose that corrections should be applied in all clear cases of sensor misalignment and when the frame of reference changes spatially and temporally however no corrections should be used where different flow velocity vector orientations not sensor misalignment are responsible for the mean vertical velocity differing from zero

detection and reconstruction of large scale coherent flow structures in gravel bed rivers large scale flow structures lsfs in the streamwise direction are important features of gravel bed river flows because they may contribute to sediment transport and gas exchange in the present study these structures are detected using huang s empirical mode decomposition and reconstructed with phase averaging techniques based on a hilbert transform of the velocity signal the analysis is based on the fluctuating component of 15 quasi instantaneous velocity profiles measured with a three dimensional 3d acoustic doppler velocity profiler advp in an armoured gravel bed river with a low relative submergence of 2 9 ratio between flow depth and bed grain diameter lsfs were identified in most of the measured profiles and consistently showed similar features we were able to characterize the geometry of these large scale coherent structures the front has a vertical linear shift in the time domain and a vertical profile corresponding to a first quarter moon with the apex situated at z h approximate to 0 4 in the vertical the front scales with flow depth h and in the streamwise direction lsfs scale with three to seven times the mean flow depth on the bed the effect of lsfs is a periodic non linear variation of the friction velocity on average between 0 90 and 1 10 times the mean value a model for the friction velocity cycle resulting from lsfs oscillation is presented copyright c 2014 john wiley sons ltd

turbulence spectra from the viscous sublayer and buffer layer at the ocean floor an experiment conducted on the oregon continental shelf has provided measurements of velocity fluctuations in the viscous sublayer and buffer layer of the boundary layer flow spectra from the viscous sublayer collapse considerably when scaled as suggested by bakewell lumley 1967 and buffer layer spectra collapse reasonably well with laboratory spectra when the scaling customarily used in the logarithmic layer is applied however in spite of the usefulness of the spectral scaling the scaled sublayer and buffer layer spectra from the ocean floor fall below the scaled laboratory spectra in the energy containing portion of the spectrum perhaps because the sea floor is not perfectly planar

genesis of pyrite au as zn bi te zones associated with cu au skarns evidence from the big gossan and wanagon gold deposits ertsberg district papua indonesia the ertsberg district hosts multiple skarn and porphyry related deposits which together comprise one of the largest cu au resources in the world earlier skarn cu au deposits at big gossan and 2 km along strike to the northwest at wanagon gold are overprinted by distinctive late stage pyrite sphalerite arsenopyrite and native gold with local bi and te minerals the wanagon gold deposit contains an estimated 2 million ounces moz of gold reserves at big gossan are 33 million tonnes mt at 2 63 percent cu 0 92 g t au and 15 72 g t ag phlogopite from the big gossan occurrence is younger than 2 82 0 04 ma based on a new 40ar 39ar age from the big gossan skarn and k feldspar from the wanagon gold deposit has a 40ar 39ar age of 3 62 0 05 ma a k ar date 3 81 0 06 ma from the wanagon sill constrains formation of the overprinting skarn cu au and late stage wanagon gold deposit to a period of ca 0 2 m y at big gossan earlier skarn cu au mineralization displays three dimensional mineralogical chemical and temperature zonation the high temperature core defined by low zn cu plunges to the northwest and is open at depth highest cu grades and greatest development of the overprinting pyrite au as zn bi te association occur to the northwest coincident with northeast striking faults pyrite au as zn bi te occurrences are also distributed in faults and fractures to the north and south of the big gossan skarn cu au deposit at wanagon gold leaching of skarn and sandstone preceded introduction of the pyrite au as zn bi te occurrences in the sandstone the pyrite au as zn bi te mineralization was accompanied by k feldspar adularia and minor quartz gangue in carbonate rocks no leaching or secondary k feldspar is apparent instead sulfides are accompanied by quartz and dolomite gangue the delta 34s of sulfide from skarn cu au and overprinting pyrite au as zn bi te occurrences at both deposits range from 0 7 to 5 1 per mil laser ablation inductively coupled plasma mass spectrometry la icpms analyses show that later pyrite overprinting both occurrences is distinct from that in the earlier skarn cu au deposits and contains up to 60 ppm au 2 percent as 680 ppm bi and 40 ppm te the mineralogy of the overprinting occurrences includes native gold argentian tetrahedrite and tennantite a silver antimony sulfide and bi and te ag au minerals including cosalite bismuthinite petzite hessite altaite and tetradymite the fineness of native gold varies with sulfide association the lowest fineness gold 737 863 occurs with pb minerals galena and sulfosalts and the higher fineness gold 904 974 occurs trapped within pyrite or in association with bismuthinite fluid inclusions in sphalerite and quartz in the big gossan pyrite au as zn bi te occurrence have an average salinity of 8 wt percent nacl equiv and an average homogenization temperature of 245 c stable isotopes indicate that the inclusion fluids were magmatic however a direct genetic relationship to earlier skarn cu au mineralization is not obvious the pyrite au as zn bi te occurrences are considered to have formed from a fluid with a different composition possibly the magmatic precursor to fluids commonly recognized in low and high sulfidation epithermal deposits that develops at shallow levels and contains significant nonmagmatic i e meteoric water

different crustal sources for au rich and au poor ores of the grasberg cu au porphyry deposit abstract the grasberg is a porphyry copper deposit that is crosscut by a second stage mineralization which is greatly enriched in gold sulfides from the porphyry type event yield a 2 9 0 3 ma re os isochron that agrees with published geochronology the initial 187os 188os ratio of the isochron is 0 56 0 02 and implies a significant crustal component for the source of os and by inference the other base metals the samples from the crosscutting secondary event do not form an isochron but form a mixing line with the older porphyry style mineralization as one of the end members and a very radiogenic end member possibly shale the initial 187os 188os ratios from samples of the second event range from 0 81 to 1 26 and correlate with gold content the most radiogenic samples have the highest gold the re os isotope data indicate different crustal sources for the ore forming elements at the grasberg cu au deposit and support a model in which gold is derived from sedimentary protoliths that may have been pre enriched by sedimentary processes the gold derived from these sources is concentrated by magmatic hydrothermal systems the requirement of a sedimentary source for gold to produce hydrothermal gold deposits has been debated for decades and this study provides strong support for the model

a detrital model for the origin of gold and sulfides in the witwatersrand basin based on re os isotopes abstract the re os systematics of gold and sulfides from the witwatersrand basin were utilized to determine whether the gold is detrital or was introduced by hydrothermal solutions from outside the basin gold from a gravity concentrate from the western areas gold plant and gold from the vaal reef have very high os concentrations of approximately 73 to 10000 ppb and 3 to 32 ppb re resulting in 187re 188os ratios of 0 010 to 0 185 the gold has subchondritic 187os 188os ratios between 0 1056 to 0 1099 and an average value of 0 1067 rhenium depletion ages trd range from 3 5 ga to 2 9 ga with a median age of 3 3 ga pyrite from the vaal reef have os concentrations ranging from 0 26 to 0 68 ppb re concentrations of 1 7 to 2 8 ppb and187re 188os ratios of approximately 14 to 87 the pyrite samples have measured 187os 188os ratios of 0 84 to 4 7 and define an isochron with an age of 2 99 0 11 ga mswd 0 77 the os isotopic data from the direct measurement of gold preclude introduction of gold to the witwatersrand basin from crustally derived metamorphic or hydrothermal fluids between 2 7 to 2 0 ga the unradiogenic 187os 188os ratios old trd ages of the western areas and vaal reef gold samples as well as the contemporaneously old age of the vaal reef pyrite are consistent with detrital deposition of gold during the formation of the witswatersrand basin the os data will allow for minor hydrothermal remobilization and or overprinting of hydrothermal gold on preexisting detrital gold grains but does not support the introduction of gold solely by hydrothermal fluids

turbulence at a roughness transition in a depth limited flow over a gravel bed turbulence statistics derived from velocity measurements along a longitudinal transect characterized by a roughness transition are presented the bed morphology along the transect is dominated by composite scales of roughness ranging from an armoured bed in the upstream section to the presence of large protuberant clasts superimposed on the bed in the downstream section an array of four electromagnetic current meters operating at a frequency of 20 hz was used to measure the longitudinal and vertical velocities at various heights above the bed surface and at different positions along the transect emphasis is put on the longitudinal and vertical distributions of turbulent flow statistics such as reynolds shear stress uv cross correlation and quadrant analysis of velocity fluctuations the results indicate that the presence of protuberant clasts modifies the turbulence structure increases turbulence intensity and appears to dominate turbulence generation distinct flow zones are observed in particular a clear distinction is made between i a sublayer below the top of the major roughness elements identified by fluid motions predominantly towards the bed surface and characterized by intense eddying with some vortices or rollers possibly being trapped in this near bed flow region and ii an inner layer located immediately above the major protuberant clasts identified by positive vertical velocities and hence upward directed fluid motion the dominant generative mechanism of flow structure appears to be the shedding of vortices from the lee of obstacles interaction of vortices stretched by shear into the main body of flow downstream from major obstacles dominates the turbulence structure in depth limited flows over coarse and irregular bed surfaces

role of near bed turbulence structure in bed load transport and bed form mechanics the interactions between turbulence events and sediment motions during bed load transport were studied by means of laser doppler velocimetry and high speed cinematography sweeps u 0 w 0 w 0 which contribute negatively to the bed shear stress and are relatively rare individually move as much sediment as sweeps of comparable magnitude and duration however and much more than bursts u 0 and inward interactions u 0 w 0 when the magnitude of the outward interactions increases relative to the other events therefore the sediment flux increases even though the bed shear stress decreases thus although bed shear stress can be used to estimate bed load transport by flows with well developed boundary layers in which the flow is steady and uniform and the turbulence statistics all scale with the shear velocity it is not accurate for flows with developing boundary layers such as those over sufficiently nonuniform topography or roughness in which significant spatial variations in the magnitudes and durations of the sweeps bursts outward interactions and inward interactions occur these variations produce significant peaks in bed load transport downstream of separation points thus supporting the hypothesis that flow separation plays a significant role in the development of bed forms

effects of turbulence on the transport of individual particles as bedload in a gravel bed river this study investigates the association between mean and turbulent flow variables and the movement of individual particles in a gravel bed river the experimental design implemented in the eaton north river quebec canada is based on the simultaneous observations at a high temporal resolution of both particle movements as bedload using an underwater video camera and of the streamwise and vertical flow velocity components using a vertical array of three electromagnetic current meters ecms the frequency and distance of displacement of particles larger than 20 mm that were sliding or rolling on the bed were measured from a 10 minutes long film mean and turbulent flow properties obtained for periods without sediment transport are compared to those when particles were sliding and rolling when particles are sliding weak differences are present for the mean streamwise velocity and normal vertical stresses instantaneous reynolds shear stresses are significantly lower for sliding events which was not expected but could be explained by the important dominance of quadrant 3 events inward interactions when particles are rolling only the vertical normal stresses show a weak difference from those observed in the absence of transport but they tend to occur when quadrant 2 ejections dominate the flow field for both sliding and rolling particles vertical and or streamwise fluid accelerations show high magnitude values when compared to periods without transport for sliding particles streamwise acceleration is mostly negative and combines most of the time with a positive vertical acceleration for rolling particles streamwise and vertical acceleration are predominantly of opposite sign these results suggest that fluid acceleration or deceleration in the streamwise and vertical directions is affecting the pressure field around particles in this study fluid acceleration seems to play a more important role than reynolds shear stress or normal stresses for bedload movements copyright 2010 john wiley sons ltd

comparisons between acoustic measurements and predictions of the bedload transport of marine gravels continuous detailed records of marine gravel transport have been obtained acoustically and compared with bedload transport rates qb predicted by five bedload transport equations using measurements of the near bed turbulent current flow when mean flow data are used in these equations total qb estimates are similar to those measured however when instantaneous flow data are used total qb is over estimated by approximately one order of magnitude based on the acoustic measurements an empirical equation has been obtained that gives accurate estimates of total qb over a tidal cycle and simulates well the intermittent characteristics of marine bedload transport

the osmium isotopic composition of organic rich marine sediments abstract the osmium os concentration and 187 os 186 os ratio of several recent marine organic rich sediment samples from three widely separated sites have been measured os concentrations range from 0 095 to 0 212 ppb and 187 os 186 os ratios range from 8 2 to 8 9 the calculated fraction of hydrogenous os exceeds 78 in all samples thus the 187 os 186 os ratio of these samples reflects os isotopic composition of seawater the small range in measured 187 os 186 os ratio indicates that the os isotopic composition at these sites is fairly homogeneous the large magnitude of the os burial flux at these sites indicates the os burial in association with organic rich sediments is an important sink in the marine cycle of os these data also suggest that ancient organic rich sediments may provide a record of past variations in the os isotopic composition of seawater

turbulent perturbations of velocity in the conwy estuary abstract field measurements of the vertical and horizontal components of fluid velocity 0 43 m above the bed have been made with an electromagnetic flowmeter in a partially mixed reach of the conwy estuary for parts of a flood and an ebb tide the turbulent mean velocity and density fields showed different effects for flood and ebb tides caused by the interaction of shear and the longitudinal density gradient the turbulent velocity parameters were generally dominated by bed generated turbulence effects but significant longer period contributions attributed to the shear density interactions were detected the shear stress measurements made by two independent methods showed good agreement the results generally show good agreement with previous less complete data the use of the richardson number to quantify vertical stability needs further consideration for partially mixed estuarine flows

copper isotopic zonation in the northparkes porphyry cu au deposit se australia abstract significant systematic cu isotopic variations have been found in the northparkes porphyry cu au deposit nsw australia which is an orthomagmatic porphyry cu deposit copper isotope ratios have been measured in sulfide minerals chalcopyrite and bornite by both solution and laser ablation multi collector inductively coupled plasma mass spectrometry mc icp ms the results from both methods show a variation in 65cu of hypogene sulfide minerals of greater than 1 relative to nist976 significantly the results from four drill holes through two separate ore bodies show strikingly similar patterns of cu isotope variation the patterns are characterized by a sharp down hole decrease from up to 0 8 0 29 0 56 1 n 20 in the low grade peripheral alteration zones phyllic propylitic alteration zone to a low of 0 4 0 25 0 36 1 n 30 at the margins of the most mineralized zones cu grade 1 wt in the high grade cores of the systems the compositions are more consistent at around 0 2 0 19 0 14 1 n 40 the cu isotopic zonation may be explained by isotope fractionation of cu between vapor solution and sulfides at high temperature during boiling and sulfide precipitation processes sulfur isotopes also show an isotopically light shell at the margins of the high grade ore zones but these are displaced from the low 65cu shells such that there is no correlation between the cu and s isotope signatures fe isotope data do not show any discernable variation along the drill core this work demonstrates that cu isotopes show a large response to high temperature porphyry mineralizing processes and that they may act as a vector to buried mineralization

a re os isotope study of sedimentary rocks and copper gold ores from the ertsberg district west papua indonesia abstract the ores of the ertsberg district consist of both porphyry stockwork and contact controlled mineralization related to the grasberg and ertsberg intrusion centers high grade copper mineralization with gold occurs in skarns on the periphery of each of the intrusion centers the periphery mineralization includes the kucing liar skarn related ores the massive sulfide lenses on the borders of the grasberg intrusive complex and the giant skarn bodies of the deep and intermediate ore zones together with the ores of the dom complex on the margin of the ertsberg diorite the ertsberg orebody the basis of discovery of the district is a copper gold roof pendant of sedimentary strata in the diorite in order to clarify genetic and geochronologic links between the peripheral sediment hosted ore bodies and the intrusion hosted ore bodies re os isotopes of the ores and subjacent precambrian and phanerozoic crust were analyzed re os geochronology of molybdenites was used to resolve the age relationships of the ore bodies the grasberg and kucing liar molybdenites have older molybdenite mineralization ages of 2 88 0 02 ma and 3 01 0 02 ma respectively whereas the ertsberg molybdenite has a younger age of 2 54 0 02 ma these data agree with ar chronologies of the alteration associated with mineralization pollard and taylor 2000 pollard p j taylor r 2000 geochronology of intrusive rocks and cu au mineralization in the ertsberg district in proceedings of freeport institut teknologi bandung itb geological symposium bandung java pp 17 19 and also indicate that the grasberg and kucing liar molybdenites are closely similar in age and older than the ertsberg intrusive system re os data from pyrite chalcopyrite magnetite gold and the surrounding sedimentary rocks from the district define a mixing relationship between samples from the initial stockwork mineralization and peripheral ores of each intrusion center sulfide and oxide minerals from primary stockwork mineralization are isotopically homogeneous and define trends on isochron diagrams with distinct os initial ratios whereas sulfides and oxides taken from peripheral ores are isotopically heterogeneous and define trends on mixing diagrams one possible end member for the mixing is sedimentary rock surrounding the porphyries the measured os ratios of the sedimentary rocks range from 0 52 to 2 21 and overlap the os initial ratios of the sulfides and oxides sampled from both stockwork and contact mineralization the data suggest a model in which the continental crust supplied some of the os and by inference other metals during magma genesis in the lower crust and the remainder came from sedimentary rocks near the intrusion centers

generation of metal rich felsic magmas during crustal anatexis we show that partial melting of a preexisting mineral deposit during regional anatexis is likely to lead to incorporation of sulfide melt into silicate melt simple dissolution of metals in silicate melt during anatexis leads to minor metal addition to escaping magma but physical entrainment of sulfide melt can lead to extreme enrichment and higher total metal incorporation metal enrichment is enhanced if melt segregation is structurally driven only dissolved metal is incorporated if initial segregation is driven by buoyancy alone however once encapsulated within a larger volume of silicate melt immiscible globules of sulfide melt are physically carried by buoyantly rising magma gradual dissolution of entrained sulfide melt globules is expected as the silicate magma migrates from the lower crust this process may lead to significant variations in metal contents of silicate magmas above regions that underwent anatexis

in situ acoustic measurements of marine gravel threshold and transport measurements of the nearbed turbulent current flow and the bedload transport of marine gravel have been made over three tidal cycles the turbulence in the bottom boundary layer was measured using two electromagnetic current meters and the gravel transport was measured using a passive acoustic system which monitored the interparticle collision noise of locally mobile material visual estimates of bedload were also obtained with an underwater tv camera the acoustic technique unlike a conventional bedload sampler has allowed estimates of transport to be obtained with a temporal resolution comparable with the turbulence data collected this has enabled a detailed comparison to be made between the turbulent flow and the sediment response to the instantaneous flow conditions the results of the study show that of the turbulent bursting events which contribute towards the reynolds stress only the sweeps and outward interactions play a significant role in the transport of coarse sedimentary material the measurements show that it is the instantaneous increases in the horizontal turbulent velocity fluctuations that generate excess shear stresses which drive the transport process

measuring the in situ erosion shear stress of intertidal sediments with the cohesive strength meter csm the shear resistance of muddy sediments directly governs the susceptibility of the sediment to erosion by tidal and wave induced currents measurements of the natural erosion shear stress are important in modelling estuarine systems and in determining the possible impact of human disturbance a second generation erosion instrument the cohesive strength meter csm designed to measure the critical erosion shear stress ocr of intertidal sediments in situ is described the csm allows measurements of small scale spatial and temporal variation of sediment stability to be made on a scale and rapidity previously unachievable new features of specialized hardware are described and the instrument is empirically calibrated in terms of an equivalent horizontal bed shear stress using quartz sand some example results from recent field trials on the konigshafen sylt romo bight are presented the erosion characteristics of this intertidal flat varied on a cm scale due to the presence of patchy diatom biofilms areas with a diatom biofilm were more stable than those without giving a biostabilization index of 6 2

matrix rheology effects on reaction rim growth i evidence from orthopyroxene rim growth experiments the rim forming reaction quartz olivine orthopyroxene is used to investigate the effect of matrix rheology on rim growth rates orthopyroxene rim growth around olivine grains in quartz matrix is compared to rim growth around quartz grains in an olivine matrix at constant p t within one single capsule orthopyroxene rims grow faster around quartz clasts in olivine matrix than around olivine clasts in quartz matrix fourier transform infra red spectra indicate that the entire samples are water saturated because of water adsorption on the reactant grain surfaces the increased orthopyroxene growth rates in olivine matrix as opposed to quartz matrix are interpreted in terms of matrix rheology where in the two different matrix inclusion arrangements the olivine matrix behaves softer and the quartz matrix more rigid the strain energy associated with accommodation of the negative reaction volume is higher for the quartz than the olivine matrix and reduces the free energy that drives orthopyroxene rim growth growth textures in both kinds of orthopyroxene rims indicate that the diffusivity of mgo slightly exceeds the diffusivity of sio2 the relative mobility of mgo and sio2 at given p t fh2o seems to be controlled by energy minimization during orthopyroxene growth at the compressive ol opx interface our experiments provide evidence for two previously overlooked effects relevant to rim growth reactions in metamorphic rocks i diffusivity along chemical potential gradients to reaction sites is a function of rheology and ii the relative diffusivity of components during reaction rim or corona growth is a function of local volume changes at the rim s interfaces

dynamics of a river channel confluence with discordant beds flow turbulence bed load sediment transport and bed morphology 1 river channel confluences play a major role in the dynamics of all fluvial systems and yet our understanding of bed load routing at these sites is very sparse the dynamics of confluences are a function of the momentum ratio between the combining flows and the three dimensional geometry of the junction recent experiments have shown that discordance in bed height between the confluent rivers increases turbulence intensity and enhances upwelling of flow within the confluence however the significance of these flow characteristics on sediment transport is still unknown to examine the relations between flow and sediment transport we have measured near bed flow turbulence bed load transport rates and changes in bed morphology for eight different flow conditions at a sand bed discordant confluence detailed analysis of the near bed flow patterns reveals that within the shear layer low mean flow velocities are combined with the highest values of reynolds shear stresses and that turbulence generation is associated with intense upward movements of flow high sediment transport rates are found at the edges of the shear layer region where horizontal vertical cross stresses uw are high these patterns match changes in bed morphology where erosion occurs along the shear layer the relation between the shear layer and sediment transport confirms the role of bed discordance on the dynamics of the confluence migration of the shear layer into the confluence as a result of a change in momentum ratio modifies local near bed flow characteristics sediment transport rates and the spatial distribution of deposition and erosion zones

zircon and molybdenite geochronology and geochemistry of the kalmakyr porphyry cu au deposit almalyk district uzbekistan implications for mineralization processes abstract copper gold and molybdenum mineralization of the kalmakyr porphyry deposit in uzbek tien shan occurs as stockworks veinlets and disseminations in the phyllic and k silicate alteration zones developed predominantly in a middle to late carboniferous intrusive complex composed of monzonite and granodiorite porphyry zircon u pb dating yielded an age of 327 2 5 6 ma for the ore hosting monzonite and an age of 313 6 2 8 ma for the ore bearing granodiorite porphyry re os dating of seven molybdenite samples from stockwork and veinlet ores yielded model ages from 313 2 to 306 3 ma with two well constrained isochron ages of 307 6 2 5 ma five stockwork ores and 309 1 2 2 ma five stockwork ores and two veinlet ores respectively these results indicate that cu au mineralization post dated the emplacement of the monzonite started right after the emplacement of the granodiorite porphyry and lasted for ca 7 ma afterward the geochronological and geochemical data suggest that the kalmakyr deposit was formed in a late carboniferous mature magmatic arc setting probably related to the latest subduction process of the turkestan ocean beneath the middle tien shan the e hf t values of zircon grains from the monzonite vary from 11 to 1 7 with an average of 5 1 and those of zircon grains from the granodiorite porphyry range from 5 7 to 1 8 with an average of 2 4 these data indicate that the magma of both monzonite and granodiorite porphyry was derived from partial melting of a thickened lower crust with input of mantle components and variable crustal contamination and that there was more mantle contribution to the formation of the monzonite than the granodiorite porphyry the high rhenium concentrations of molybdenite 98 899 ppm also indicate major mantle contribution of rhenium and by inference ore metals the relatively high eu n eu n values average 0 68 ce 4 ce 3 values average 890 and ce nd values average 36 8 for zircon grains from the granodiorite porphyry than those from the monzonite average eu n eu n 0 33 average ce 4 ce 3 624 average ce nd 3 9 suggest that the magma for the syn mineralization granodiorite porphyry has higher oxygen fugacity than that for the pre mineralization monzonite based on these data it is proposed that while the monzonite was emplaced the oxygen fugacity and volatile contents in the magma were relatively low and ore metals might disperse in the intrusive rock whereas when the granodiorite porphyry was emplaced the oxygen fugacity and volatile contents in the magma were increased favoring copper and gold enrichment in the magmatic fluids the kalmakyr deposit formed from a long lived magmatic hydrothermal system connected with fertile magmatic sources in relation to the subduction of the turkestan ocean beneath the middle tien shan

geochemical and geochronological constraints on the formation of shear zone hosted cu au bi te mineralization in the stanos area chalkidiki northern greece abstract copper gold bismuth tellurium mineralization in the stanos area chalkidiki peninsula greece occurs in the proterozoic to silurian aged serbomacedonian massif which tectonically borders the mesozoic circum rhodope metamorphic belt to the west and crystalline rocks of the rhodope massif to the east this area contains the paliomylos chalkoma and karambogia prospects which are spatially related to regional nw se trending shear zones and hosted by marble amphibolite gneiss metagabbro and various muscovite biotite chlorite actinolite feldspar quartz schists of the silurian vertiskos unit metallic minerals occur as disseminated to massive aggregates along foliation planes and in boudinaged quartz veins iron bearing sulfides pyrite arsenopyrite and pyrrhotite formed prior to a copper bearing stage that contains chalcopyrite along with galena sphalerite molybdenite and various minerals in the system bi cu pb au ag te fluid inclusion homogenization temperatures of primary aqueous liquid vapor inclusions in stage i quartz veins range from 170 1 c to 349 6 c peak at 230 c with salinities of 4 5 to 13 1 wt nacl equiv calculated isochores intersect p t conditions associated with the upper greenschist facies caused by local overpressures during late stage tectonic movement along the shear zone in the eocene which produced stretching and unroofing of rocks in the region values of 34 s for sulfides in the stanos shear zone range from 2 42 to 10 19 and suggest a magmatic sulfur source with a partially reduced seawater contribution for fluids in equilibrium with quartz 18 o at 480 c varies from 5 76 to 9 21 but does not allow for a distinction between a metamorphic and a magmatic fluid a 187 re 187 os isochron of 19 2 2 1 ma for pyrite in the paliomylos prospect overlaps ages obtained previously from intrusive rocks spatially related to the skouries porphyry cu au the asimotrypes au and the intrusion related palea kavala bi te pb sb au deposits in northern greece as well as alteration minerals in the carbonate replacement madem lakkos pb zn deposit ore forming components of deposits in the stanos area were likely derived from magmatic rocks at shallow depth that intruded an extensional shear environment at 19 ma

laboratory investigation of turbulent flow structure around a bed mounted cube at multiple flow stages this research compares the spatially distributed turbulent wake characteristics associated with a submerged bed mounted cube at three flow stages the experiments were conducted in a large laboratory flat bed flume at high reynolds numbers the velocity gradient under each flow condition was kept near constant which yielded novel data that isolated the effect of flow depth on turbulent flow structure in the wake spatially distributed instantaneous three dimensional velocities were recorded using multiple acoustic doppler velocimeters advs with decreasing relative depth marked variations in the spatial distributions of mean and turbulence statistics were observed that have important implications for local sediment mobility and fish habitat

metallogenic potential of porphyries in tulasu basin northwest tianshan insight from magma nature and crustal thickness abstract tulasu basin in northwest tianshan hosts a lot of late paleozoic epithermal deposits such as axi jingxi yelmand and tawuerbieke deposits epithermal deposits are considered as telescoped systems of porphyry deposits however porphyry deposits are not discovered in tulasu basin though granitoid porphyries are widespread in this region tulasu pluton complex as one of the largest intrusions located in northeast part of tulasu basin is composed of the late devonian quartz diorite porphyry and pyroxene diorite porphyry and the late carboniferous granodiorite porphyry and granite porphyry the metallogenic potential of each rock type is evaluated in terms of magma nature and crustal thickness of source the magma nature including magmatic oxygen fugacity and water content is estimated based on trace elements compositions of zircons amphibole hygro barometer and ilmenite magnetite mineral pairs the mean ce4 ce3 ratio magmatic oxygen fugacity and water content of the late devonian quartz diorite porphyry are 291 fmq 1 0 1 8 fmq 0 2 1 5 and 0 9 2 2 wt respectively while those of pyroxene diorite porphyry are 96 fmq 2 6 3 3 and 0 2 1 3 wt the late carboniferous granodiorite porphyry has a mean ce4 ce3 ratio of 138 the crustal thicknesses in the tulasu area are estimated to be 30 35 km at the late devonian and 40 km at the late carboniferous based on whole rock geochemistry of the late devonian dioritic rocks and the late carboniferous granitic rocks considering magmas associated with typical porphyry deposits which have high oxygen fugacity of fmq 1 5 to 3 and water content 4 5 wt and are derived from crustal thickness of 30 km we think both dioritic and granitic rocks of tulasu porphyries have favorable conditions of oxidation state and crustal thickness for porphyry deposit formation however the magmatic water contents of these rocks are relatively low therefore the tulasu porphyries have low potential in forming porphyry cu deposits

fine scale characterization of the turbulent shear layer of an instream pebble cluster this study characterizes the shear layer and associated vortex shedding around an isolated submerged pebble cluster in a gravel bed river the approach combines flow visualization and high frequency three dimensional velocity acoustic doppler velocimeter measurements two vortex shedding modes in the wake of the cluster were identified a small scale high frequency initial instability mode and a lower frequency mode that scales with cluster height the lower frequency mode arose from the intermittent interaction and amalgamation of the small scale instability vortices reynolds shear stresses velocity spectra and coherence functions indicated a dominance of longitudinal vertical shedding vortices in the wake of the cluster simultaneous flow visualization was required to determine the nature and behavior of the shedding modes quadrant analysis revealed that q2 and q4 events contributed 80 of the local longitudinal vertical component reynolds shear stress and demonstrated a dominance of ejection events in the wake of the cluster through flow visualization the behavior of the shear layer was seen to vertically expand and contract with the passage of q2 and q4 events respectively

controls on gold solubility in arc magmas an experimental study at 1000 c and 4 kbar in order to 1 explain the worldwide association between epithermal gold copper molybdenum deposits and arc magmas and 2 test the hypothesis that adakitic magmas would be au specialized we have determined the solubility of au at 4 kbar and 1000 c for three intermediate magmas two adakites and one calc alkaline composition from the philippines the experiments were performed over a fo2 range corresponding to reducing not vert similarnno 1 moderately oxidizing not vert similarnno 1 5 and strongly oxidizing not vert similarnno 3 conditions as measured by solid ni pd o sensors they were carried out in gold containers the latter serving also as the source of gold in presence of variable amounts of h2o and in a few additional experiments of s concentrations of au in glasses were determined by la icpms gold solubility in melt is very low 30 240 ppb but increases with fo2 in a way consistent with the dissolution of gold as both au1 and au3 species in the s bearing experiments performed at not vert similarnno 1 gold solubility reaches much higher values from not vert similar1200 to 4300 ppb and seems to correlate with melt s content no systematic difference in gold solubility is observed between the adakitic and non adakitic compositions investigated oxygen fugacity and the sulfur concentration in melt are the main parameters controlling the incorporation and concentration of gold in magmas certain adakitic and non adakitic magmas have high fo2 and magmatic s concentrations favorable to the incorporation and transport of gold therefore the cause of a particular association between some arc magmas and au cu mo deposits needs to be searched in the origin of those specialized magmas by involvement of au and s rich protoliths the subducted slab which contains metal rich massive sulfides may constitute a potentially favorable protolith for the genesis of magmas specialized with respect to gold

tectonic implications from re os dating of mesozoic molybdenum deposits in the east qinling dabie orogenic belt abstract the east qinling dabie molybdenum belt is part of a larger east west trending metallogenic belt in eastern china most of the molybdenum deposits occur as porphyry or porphyry skarn type but there are also some vein type deposits following systematic re os dating of molybdenite from 13 deposits and comparisons with two previously dated deposits we have recognized that the molybdenum mineralization in the east qinling dabie belt was developed during hydrothermal activity linked to magmatism and the emplacement of granitoid stocks three pulses of granitoid magmatism and mo mineralization are recognized corresponding to significant tectonic events in the east qinling dabie belt vein type deposits dated at 233 221 ma were formed in detachment fractures indicating localized extension within the collisional setting of the north china and yangtze cratons i type and transitional i and s type granites and related mineralization dated at 148 138 ma may have formed part of a continental magmatic arc with widespread magmatism and back arc extension caused by subduction of the izanagi or paleopacific plate beneath the eurasian continent in a wnw ese direction in the late jurassic early cretaceous both s type and transitional s and i type granite associated porphyry molybdenum deposits dated at 131 112 ma are part of an extensive mineralization event throughout east china that can be ascribed to regional large scale lithospheric thinning delamination and thermal erosion

re os isotope geochemistry of tertiary picritic and basaltic magmatism of east greenland constraints on plume lithosphere interactions and the genesis of the platinova reef skaergaard intrusion abstract re os abundance and isotopic studies on a small number of samples from the lowermost part of the east greenland lava pile and the nearby skaergaard intrusion show that picrite and ankaramite lavas tend to have high os abundances and low re os ratios with most rocks having near chondritic values for initial 187 os 188 os one olivine basaltic sample with very high 187 os 188 os has most likely been affected by upper crustal contamination there is no clear evidence for recycled crustal material in the ancestral iceland plume source or for a significant degree of interaction of the picrites with ancient subcontinental lithospheric mantle of the north atlantic craton the platinova reef the precious metal enriched zone in the skaergaard intrusion has very high au and pd contents but very low pt and os contents compared to platiniferous horizons in other layered intrusions these characteristics are almost certainly due to the very late stage in the evolution of the skaergaard magma chamber at which the platinova reef formed the platinova reef yields a re os tchur model age that is younger than the age of the intrusion which was most likely produced by some form of post depositional disturbance to the re os isotopic system the high pge contents of the east greenland volcanic rocks indicate that they were formed from magmas that had the potential to form major accumulations of ni cu pge sulphide deposits had similar magmas undergone significant interaction with continental crust elsewhere in east greenland they may have formed massive magmatic sulphide deposits thus the potential for the discovery of large magmatic sulphide deposits of the noril sk talnakh type in east greenland must be considered excellent

measurements of turbulence in the benthic boundary layer over a gravel bed it is now generally recognized that the mathematical description of sediment dynamics will be improved through an understanding of geophysical turbulence in this study therefore the turbulence characteristics of the benthic boundary layer over coarse sediments are examined as a step towards the realization of such a description examination of the turbulence has been conducted using spectral correlation quadrant and statistical analyses and a number of features have been identified mean eddy length scales obtained using spectral and autocorrelation techniques were found to be similar the interpretation of the duration and interval between the intermittent bursting events scaled using outer flow variables was found to be dependent upon the sampling interval autocorrelation analysis revealed a high correlation between bedload transport and the instantaneous horizontal flow component rather than instantaneous kinematic stress from the standpoint of developing prognostic transport models based on physically realistic benthic flow processes it is considered that turbulence measurements will lead to such formulation

magma sources and gold mineralisation in the mount leyshon and tuckers igneous complexes queensland australia u pb and hf isotope evidence abstract in situ lam icpms u pb hf isotope and trace element analyses of zircon have been used to evaluate the relative contributions of juvenile mantle and crustal sources to the intrusive rocks of the mafic to intermediate gold poor tuckers igneous complex tic and the spatially and temporally related felsic mount leyshon igneous complex mlic which hosts a gold rich porphyry system the tic intrusions range in age from 304 2 9 1 ma to 288 5 6 4 ma and the mlic intrusions from 291 0 4 8 ma to 288 6 ma cross cutting relationships define the intrusion sequence from oldest to youngest diorite monzodiorite mafic granodiorite and biotite microgranite within the tic early dyke southern porphyry and late dyke within the mlic zircons from the earliest rock type within each complex have a wide range in hf 5 2 to 14 8 for the tic diorite 2 0 to 12 4 for the mlic early dykes suggesting the mixing of juvenile and crustal magmas this interpretation is supported by trace element data that show the presence of two distinct zircon populations in the mlic early dyke the later intrusive rocks have narrower ranges in hf typically hf units and trace element patterns of zircon this homogeneity suggests derivation from magmas produced by further mixing and fractional crystallisation of the tic diorite and the mlic early dyke magmas respectively a greater crustal contribution to the gold rich mlic is inferred from the range of median hf 3 2 to 4 5 for the mlic 5 4 to 8 7 for the tic we suggest that the mlic was derived by melting of more felsic crustal rocks and with less input from juvenile mantle then the tic it was not derived by fractional crystallisation of an intermediate to mafic tic like magma modelling of hf isotope data yields a mean model age of 1040 10 ma at 176 lu 177 hf 0 015 for the crustal component in both complexes gold was precipitated in the mlic breccia during the emplacement of the late dykes the isotopically homogenous nature of the late dykes suggests that no additional juvenile mantle input was involved at the mineralisation stage this supports a model in which gold and other metals were indigenous to the late dykes magma and were concentrated by magma differentiation and fluid evolution processes

re os systematics of sulfides chalcopyrite bornite pyrite and pyrrhotite from the jiama cu mo deposit of tibet china abstract the jiama cu mo deposit one of the largest skarn porphyry deposits in china currently being mined is located in the eastern part of the gangdese porphyry cu belt tibet china chalcopryite and bornite concentrate in the skarn ore zone at jiama with molybdenite concentration whereas molybdenite occurs in the porphyry ore zone and hornfels ore zone relatively by itself cu and mo have different distributions in the porphyry ore zone with cu concentrating above the porphyry and with mo inside of porphyry intrusion the direct re os dating on cu sulfides will be helpful for us to understand the cu and mo mineralization at jiama this study is the first attempt to use the re os isotope system to directly date chalcopyrite bornite pyrite and pyrrhotite at jiama the contents of re common os and 187 os in these four sulfides are 0 145 32 9 ppb 0 0022 0 0669 ppb and 0 0003 0 0118 ppb respectively they have very low ratios of 187 os to common os 0 09 0 55 therefore they are different from low level highly radiogenic llhr sulfides the plot of 187 re 188 os and 187 os 188 os did not yield an isochron age based on the scatter points even if age of 15 ma based on molybdenite re os age is used to calculate the initial 187 os 188 os the ratios show a wide range and low ratios of 187 re 188 os 187 os 188 os the geology suggests the cu and mo mineralizations at jiama are both related to porphyry intrusions and the cu mineralization should also have occurred in miocene based on the molybdenite re os age and porphyry zircon u pb ages

re os systematics of pyrite from the bolcana porphyry copper deposit apuseni mountains romania we report here the results of a re os study of the bolcana porphyry copper cu au deposit in the apuseni mountains of romania the age of the deposit is known only from its spatial relationship with basement rocks of known age the mineralization has not been directly dated the re os isotope system provides an excellent means of dating the mineralization itself and may additionally place constraints on the metal source this methodology has been applied to pyrite a ubiquitous mineral because no molybdenite was found in our sampling level the results yield an age of 11 8 0 51 2 8 ma this age is in good agreement with available geochronological information the large dispersion around the age regression line which exceeds that expected from identified analytical uncertainties may result from diffusive redistribution of 187 os the low inital 187 os 188 os ratio of the least radiogenic sample may suggest a mantle dominated source common os contents are very low in all of the samples 0 6 to 17 5 ppt in contrast re contents vary considerably from 3 to 867 ppb depending on the sample location in the mineralized porphyry intrusion re is considerably enriched in the apex zone of the mineralized porphyry this accumulation could be explained by intensive boiling at the top of the porphyry which concentrates chloride in the liquid phase allowing re to be retained as re rich chloride complexes this re may then have been incorporated into the lattice of the pyrite that crystallized from the brine in stockwork veins

effects of temperature and humidity upon the transport of sedimentary particles by wind aeolian transport of sedimentary particles is a well recognized phenomenon in cold regions but the effect of low temperature t and specific humidity q upon particle entrainment has not previously been investigated this study reports on wind tunnel experiments 12 c t 32 c and 1 g kg 1 q 10 g kg 1 that suggest the aerodynamic drag required to entrain sand sized particles can be 30 lower in cold or high latitude settings as compared to hot deserts for any given regional wind velocity this effect will increase the wind strength index and thereby the proportion of time a surface is active at low temperature

very little water is necessary to make a dry solid silicate system wet the standard rim forming mineral reaction olivine quartz orthopyroxene ol qtz opx has been experimentally performed at very dry conditions i e only 20 wt ppm of water present in the sample container as a fluid and most water was hydrogen dissolved within the solid crystals reaction rates and resulting fabrics at ol qtz interfaces mimic reaction features previously known from water rich conditions tens of thousands ppm our experiment indicates that very small amounts of water tens of ppm of the entire sample are highly effective in facilitating mineral reactions where water acts as a catalyst and creates porosity that might start to migrate from the initial centers of self propagating mineral reaction if rock deformation allows the threshold between dry and wet in granulite and eclogite facies rocks is crossed once the nominally anhydrous minerals are saturated with hydrogen

relationship between copper tonnage of chilean base metal porphyry deposits and os isotope ratios re os isotopes in pyrite and chalcopyrite from early high temperature hypogene alteration assemblages in chilean porphyry copper deposits identify the source of os and by inference cu in these ore systems typical concentrations for os in both pyrite and chalcopyrite are between 7 and 30 ppt 10 12 g g and for re between 0 200 and 10 ppb 10 9 g g re os isochrons yield ages and initial 187 os 188 os ratios for the sulfides the isotopic data reflect the relative contributions of copper from the mantle and crust in chilean porphyry copper deposits seven ore deposits that reside in different tectonic terranes and represent distinct epochs of mineralization in chile were studied the initial osmium ratios of the first stage of mineralization at each of the deposits range from 0 15 to 5 these values are more radiogenic than the present chondritic mantle 0 13 and indicate significant crustal contributions of os to the magmatic and or hydrothermal systems there is a strong correspondence between the total copper content and initial os isotopic ratios in base metal porphyry deposits the larger deposits have lower initial os ratios than the smaller less significant deposits this relationship implies that larger deposits acquire a greater proportion of os from the mantle the initial os ratio of samples in the central segment of porphyry copper deposits of northern chile also decreases with decreasing age of the deposit a plausible interpretation of the re os data is that the later and larger deposits use regional tectonic and structural features that allow sampling of deeper more primitive magmatic sources

a comparison of flow intensities in alluvial rivers characteristics and implications for modelling flow processes this paper compares flow intensity data obtained with different instruments from a variety of fluvial environments it examines associations between the root mean square of longitudinal velocity fluctuations flow intensity local mean velocity relative depth and boundary resistance results indicate systematic differences in the behaviour of flow intensity which scale with respect to position in the boundary layer deep sand bedded rivers boundary grain resistance shallow river environments with coarse beds and possibly form resistance shallower sand bedded rivers preliminary approaches to prediction and modelling of variations in flow intensity are suggested based upon linear regression relationships intensity values are also compared with theoretical and empirical limits to the use of taylor s substitution which allows time and frequency properties of a single point velocity time series to be used to yield a flow length scale in general limits are exceeded in all environments for near boundary flow measurements but are met for y d 0 3 in most cases in sand bed rivers and for y d 0 4 in some gravel bed environments 1998 john wiley sons ltd

re os isotope systematics in black shales from the lesser himalaya their chronology and role in the 187os 188os evolution of seawater abstract re and os abundances and os isotope systematics have been measured in a number of black shales sampled from outcrops and two underground phosphorite mines maldeota and durmala in the lesser himalaya the re and os concentrations in these samples exhibit wide range 0 2 to 264 ng g and 0 02 to 13 5 ng g respectively with a mean re os of 25 the 187 os 188 os of these samples also show a broad range 1 02 to 11 6 with many of them far more radiogenic than the currently eroding continental crust the black shales from the maldeota and durmala mines collected a few meters above the krol tal pc c boundary and occurring in the same stratigraphic horizon yield 187 re 187 os isochron ages of 554 16 and 552 22 ma respectively consistent with fossil evidences and those assigned for the pc c boundary at various other locations these results indicate closed system behaviour of re and os in these mine samples and reaffirm the validity of 187 re 187 os pair to date organic rich sediments the age of these mine samples from the outer belt seems to be a few hundred millions of years younger than the preliminary re os age of 839 138 ma for black shales from theog collected from the inner belt these initial results lean toward the hypothesis that the inner belt sediments were deposited earlier than the outer belt however more analyses of black shales are needed to confirm this the role of weathering black shales from the himalaya in contributing to the os isotope evolution of seawater over the past 25 ma was assessed using a simple budget model for seawater os and assuming values for os fluxes and 187 os 188 os based on the available limited data on os concentration and its 187 os 188 os in rivers and oceans these calculations indicate that the required contributions from black shale weathering to account for the entire increase in oceanic 187 os 188 os over the past 16 ma is difficult to satisfy by varying only the os flux from htp rivers 187 os 188 os kept constant at 1 324 or their 187 os 188 os 188 os flux constant at today s value 131 moles yr the requirements to balance os isotope budget in ocean through weathering of black shales however is easier to accommodate if both the os flux from htp himalayan tibetan plateau rivers and their 187 os 188 os are allowed to vary measurements of os abundance in htp rivers and its isotopic composition are needed to test the validity of the model results

probabilistic description of grain resistance from simultaneous flow field and grain motion measurements experiments were carried out using a mobile gravel bed placed in a tilting flume with a modified particle image velocimetry piv system individual grain movements were surveyed using data from time series of images near bed velocity flow field measurements were made simultaneously above the same area of the sediment surface by applying cross correlation techniques to the collected plan view images statistics of grain motions were collected through a semiautomatic procedure significant changes in the flow field were observed in the proximity of the entrained or deposited particles a strong correlation is shown between the changes in the local streamwise and lateral velocity and the movement of the grains the theory of grass is revisited and developed based on the experimental results the probability distribution of individual grain resistance has been derived from the statistics of the near bed velocity field and of the entrainment risk

phanerozoic ocean cycles and sedimentary rock hosted gold ores the worldwide occurrence of au ores associated with phanerozoic strata reveals a bimodal temporal association with either older paleozoic or younger mesozoic successions these strata were deposited mostly in passive margin environments synchronously with formation of volcanogenic massive sulfide ores on active margins during times of high sea level widespread submarine oceanic volcanism reduced and at least locally sulfidic oceans and episodes of ocean anoxia this correspondence of ocean properties and ages of strata that host au seems beyond coincidence cause and effect cannot yet be described with confidence but beyond the evolution of chemically reduced strata the reduced oceans may also have been favorable to the enhancement of au in certain strata that may constitute metallotects of au

the osmium isotopic composition of the continental crust osmium isotopic compositions and concentrations have been determined for deltaic and continental shelf sediments from three major rivers the amazon changjiang and mississippi and for two loesses from the upper mississippi river valley the loesses have heavy mineral and clay compositions characteristic of mississippi river and delta sediment concentrations range from 15 to 120 pg os g and 187os 186os ratios range from 8 2 to 10 9 sediments which are polluted surface sediment from the changjiang estuary or which have scavenged metals from seawater gulf of mexico slope surface sediment and distal amazon shelf sediment have high osmium concentrations and less radiogenic isotopic compositions purely terrigenous sediments have 15 90 pg os g and 187os 186os 10 0 10 9 north american loess and mississippi delta sediment osmium isotopic compositions are indistinguishable we believe that 187os 186os 10 11 is a good average for currently eroding upper continental crust these sediments have neodymium isotopic compositions close to the global mean for river sediment terrigenous 187os 186os is significantly more radiogenic than seawater 187os 186os 8 6 requiring a nonriverine source of osmium to seawater terrigenous osmium is also significantly more radiogenic than bulk pelagic clay osmium we use the improved estimate of terrigenous 187os 186os to recalculate the flux of extraterrestrial osmium to pacific marine sediment if the residence age of osmium in an upper crustal region is similar to the neodymium model age of a sediment derived from that region a model dependent upper crustal 187re 186os ratio can be calculated for the model ages of the sediments analyzed in this study tdm 1 5 1 7 ga model 187re 186os ratios are 340 360 and can be used to correct for bias resulting from the preferential erosion of young crust the 187os 186os ratio of 2 2 ga crust with 187re 186os 400 is 14 2 we have also used the data from this study to estimate upper crustal osmium and rhenium concentrations of 50 pg g and 390 pg g respectively

geology geochronology and s pb os geochemistry of the alastuo gold deposit west tianshan nw china the alastuo gold deposit located in the narati region of the chinese west tianshan is a newly discovered gold deposit within the world class tianshan gold belt the gold mineralization is hosted by an early carboniferous granodiorite intrusion and controlled structurally by subsidiary faults of the transcrustal north narati fault the deposit consists of auriferous alteration assemblages and minor vein ores field relations and petrographic data suggest four stages of mineralization with gold precipitated coevally with quartz chlorite epidote pyrite and galena during the second and third stages that are characterized by tectonic transformation from ductile shearing to brittle deformation the temperature range of gold precipitation is estimated to be 280 330 c using chlorite geothermometry ten auriferous pyrite samples yielded a well defined re os isochron age of 325 3 ma and two sericite samples yielded plateau like 40ar 39ar ages of 321 7 3 0 ma and 321 2 2 8 ma these consistent ages suggest that the gold mineralization in the narati region was emplaced in a transitional regime from subduction to continental collision between the tarim block and middle tianshan terrane 325 310 ma rather than during the post collisional stage as in most part of the tianshan gold belt gold bearing pyrite has an initial osi value of 0 7 0 1 and lead isotopes ratios of 17 897 to 18 723 for 206pb 204pb 15 474 to 15 643 for 207pb 204pb and 37 522 to 38 299 for 208pb 204pb while samples of pyrite galena and sphalerite have 34sv cdt of 1 9 to 7 8 the isotope data suggest that the sulfur and metals are most likely derived from mixed mantle and crustal sources including metamorphic devolatilization of subducted oceanic slab and overlying sedimentary rocks the mineralization styles structural controls metal and sulfur sources and the timing of gold mineralization with respect to the orogenic event all suggest that the alastuo gold deposit represents an orogenic type deposit this newly recognized carboniferous orogenic gold mineralization event calls for a re evaluation of the gold metallogeny in the middle tianshan

evidence for mixing of re os isotopes at 2 7 ga and support of a remobilized placer model in witwatersrand sulfides and native au abstract this study analyzes re and os contents of au rich sulfides from the carbon leader tau lekoa and mponeng the vcr mponeng and tau lekoa and the black reef modder east as well as native au in the carbon leader to further investigate the detrital placer modified detrital placer and hydrothermal models for the source of au in mines from the witwatersrand an isochron plot of the results from the four locations yields an imprecise isochron age of 2381 140 ma mswd 17 and initial 187 os 188 os 0 24 0 21 isochron plots for the individual reefs also yielded ages that are younger than the deposition of the basin witwatersrand sediments samples that possess higher concentrations of os 100 ppb and low 187 re 188 os ratios to unify all of the data providing a large variation of chronologic information os mixing diagrams for both gold and sulfide minerals produce realistic mixing trends when solving os initial ratios for 2050 ma the two most probable end members for the mixing relationships are a high os concentration non radiogenic source and a low os concentration highly radiogenic source the high concentration non radiogenic os source has been measured in multiple studies and has been clearly derived from the subcontinental lithospheric mantle sclm the low concentration highly radiogenic source is debatable the measured concentrations of os in the witwatersrand ores are much greater than published os concentrations in other hydrothermal ores the data could indicate a redistribution of the detrital os signatures at 2050 ma thus a modified detrital model best explains the previously published data and this data

re os sm nd u pb and stepwise lead leaching isotope systematics in shear zone hosted gold mineralization genetic tracing and age constraints of crustal hydrothermal activity abstract a combined re os sm nd u pb and stepwise pb leaching pbsl isotope study of hydrothermal mo w bearing minerals and base metal sulfides from two adjacent shear zone hosted gold deposits ran kimberley in the harare shamva greenstone belt zimbabwe constrain the timing of the mineralizing events to two periods during an initial late archean event 2 60 ga a first molybdenite scheelite bearing paragenesis was deposited in both shear zone systems followed by a local reactivation of the shear systems during an early proterozoic 1 96 ga tectono thermal overprint during which base metal sulfides and most of the gold was re deposited while pbsl has revealed an open system behavior of the u pb systematics in molybdenite and wolframite from the ran mine initial archean re os ages are still preserved implying that this system in these minerals was more resistant to the overprint a similar retentivity could be shown for the sm nd system in scheelite and powellite associated with the above ore minerals re os isotopic data from the proterozoic mineralization in the kimberley mine point to a recent gain of re most pronouncedly affecting fe rich sulfides such as pyrrhotite a significant re loss in powellitic scheelite an alteration phase of molybdenite bearing scheelite coupled with a marked loss of u in w mo ore minerals complements the observation of a major re uptake in fe sulfides during oxidizing conditions in a weathering environment pyrrhotite under these conditions behaves as an efficient re sink lead isotope signatures from pbsl residues of molybdenite powellite and quartz indicate a continental crustal source and or contamination for the mineralizing fluid by interaction of the fluids with older sedimentary material as represented by the direct host country rocks our investigation reveals the potential of the re os isotopic system applied to crustal hydrothermal ore minerals for genetic tracing and dating purposes the simplified chemical separation of re and os from geological material used in this study together with improvements of chemical yields will enable high precision data to be collected rapidly on crustal material with low os concentrations in the future

sensitivity of bed shear stress estimated from vertical velocity profiles the problem of sampling resolution bed shear stress in open channel flows is often estimated from the logarithmic vertical velocity profile however most measuring devices used in the field do not allow for flow velocity to be measured very close to the bed the lack of near bed measurements is a critical loss of information which may affect bed shear stress estimates detailed velocity profiles obtained from a field acoustic doppler velocimeter over three different bed roughnesses clearly show that the inclusion of near bed points is critical for the estimation of bed shear stress in a shallow river environment moreover the results indicate that using the full flow depth instead of the bottom 20 per cent of the profile generates an underestimation of the shear stress when flow is uniform 1998 john wiley sons ltd

age of mineralization of the candelaria fe oxide cu au deposit and the origin of the chilean iron belt based on re os isotopes re os isotopes are used to determine the age of iron oxide cu au mineralization at candelaria chile and to explore possible genetic links with the batholithic intrusions in the area re os ages calculated from molybdenite are 114 2 0 6 ma and 115 2 0 6 ma and they are interpreted to represent the age of mineralization these ages are consistent with previously reported ages for biotite alteration that range from 114 to 116 ma an isochron calculated by re os ratios from hydrothermal magnetite and sulfides constrains an initial 187 os 188 os ratio of 0 36 0 10 the initial 187 os 188 os ratio for sulfide from bronce mine a small satellite of the candelaria orebody is 0 33 0 01 these values are broadly similar to the calculated initial 187 os 188 os ratio for magmatic magnetite in nearby batholithic rocks that range from 0 20 to 0 41 the relatively radiogenic initial 187 os 188 os ratio represents a mixture of mantle and crustal components in the ores and batholitic rocks the similarity in initial 187 os 188 os ratio of the ore and magmatic oxides suggest that the granitic plutons could be the source of metals in the candelaria district these data are consistent with the existence of a significant magmatic fluid component in the hydrothermal system as suggested by previously published work in order to establish a regional perspective we analyzed ore minerals from other chilean deposits of the iron oxide cu u au rare earth elements ree class magnetite from the manto verde iron oxide cu au deposit has os and re concentrations of 11 to 17 parts per trillion ppt and 4 to 6 parts per billion ppb respectively the initial 187 os 188 os ratio is approximately 0 20 and is similar to that of ore minerals from candelaria and of the early cretaceous batholithic intrusions these data indicate a similar metal source for the mineralization at manto verde and candelaria magnetite from three magnetite apatite deposits of the chilean iron belt have re concentrations between 0 8 and 3 ppb and os concentrations between 11 and 76 ppt calculated initial 187 os 188 os ratios of these magnetites range from 1 2 to 8 4 and are distinctly different from those of the iron oxide cu au deposits the cause of the comparatively high radiogenic signatures in the magnetite apatite ores is probably related to fluid interactions with i e leaching the surrounding sedimentary rocks during their genesis in contrast to the iron oxide cu au systems the os in magnetite apatite ores could be derived from sedimentary rocks this evidence suggests that predominantly basin derived nonmagmatic brines formed these magnetite apatite deposits

sediment generated noise and bed stress in a tidal channel 1 tidally driven currents and bed stresses can result in noise generated by moving sediments at a site in admiralty inlet puget sound washington state usa peak bed stresses exceed 20 pa significant increases in noise levels are attributed to mobilized sediments at frequencies from 4 30 khz with more modest increases noted from 1 4 khz sediment generated noise during strong currents masks background noise from other sources including vessel traffic inversions of the acoustic spectra for equivalent grain sizes are consistent with qualitative data of the seabed composition bed stress calculations using log layer reynolds stress and inertial dissipation techniques generally agree well and are used to estimate the shear stresses at which noise levels increase for different grain sizes regressions of the acoustic intensity versus near bed hydrodynamic power demonstrate that noise levels are highly predictable above a critical threshold despite the scatter introduced by the localized nature of mobilization events

estimation of flow resistance in gravel bedded rivers a physical explanation of the multiplier of roughness length the need to estimate velocity and discharge indirectly in gravel bedded rivers is a commonly encountered problem semilogarithmic friction equations are used to estimate mean velocity using a friction factor obtained from depth and grain size information although such equations have a semi theoretical basis in natural gravel bed channels an empirical constant 6 8 or 3 5 has to be introduced to scale up the characteristic grain size d50 or d84 to represent the effective roughness length in this paper two contrasting approaches are used to suggest that the multiplier of characteristic grain size is attributable to the effect of small scale form resistance reflecting the occurrence of microtopographic bedforms in gravel bedded environments first spatial elevation dependence in short detailed bed profiles from a single gravel bedded river is investigated using semivariogram and zero crossing analyses this leads to objective identification of two discrete scales of bed roughness associated with grain and microtopographic roughness elements second the autocorrelation structure of the three dimensional near bed velocity field is examined to identify regularities associated with eddy shedding and energy losses from larger grains and microtopographic bedforms apart from improving the capacity to determine friction factors for velocity and discharge estimation the findings have implications in general for the initial motion of gravelly bed material

a re os study of sulfide minerals from the bagdad porphyry cu mo deposit northern arizona usa rhenium and osmium isotopes in sulfide minerals from the bagdad porphyry cu mo deposit have been used to determine timing of mineralization and the source of osmium and by inference ore metals molybdenite chalcopyrite and pyrite were analyzed mainly from the quartz monzonite and porphyritic quartz monzonite units which are characterized by moderate to strong potassic alteration secondary biotite and k feldspar rhenium concentrations in molybdenite are between 330 and 642 ppm four re os analyses of two molybdenite samples from the quartz monzonite and porphyritic quartz monzonite yield a weighted average age of 71 8 0 2 ma 2 analyses of a third sample from a molybdenite vein in precambrian rocks outside of the main ore zone yield a weighted average age of 75 9 0 2 ma 2 and provide evidence of two separate mineralization episodes chalcopyrite samples contain 6 to 12 ppt os and 1 7 to 4 1 ppb re 187os 188os initial ratios are between 0 1 and 0 8 pyrite samples have osmium and rhenium concentrations varying in the range 8 17 ppt and 3 9 6 8 ppb respectively analyses from these pyrite samples yield an eight point isochron with an age of 77 15 ma 2 and an initial 187os 188os ratio of 2 1 0 8 mswd 0 90 the results presented here add to the growing body of work indicating that porphyry type mineralization is produced by long term multiple episodes of magmatism and associated mineralization the data also support the hypothesis that a significant part of the metals and magmas may have a crustal source as has been suggested for other copper deposits and districts in arizona

rhenium and osmium isotopes in black shales and ni mo pge rich sulfide layers yukon territory canada and hunan and guizhou provinces china rhenium and osmium abundances and osmium isotopic compositions were determined by negative thermal ionization mass spectrometry for samples of devonian black shale and an associated ni enriched sulfide layer from the yukon territory canada the same composition information was also obtained for samples of early cambrian ni mo rich sulfide layers hosted in black shale in guizhou and hunan provinces china this study was undertaken to constrain the origin of the pge enrichment in the sulfide layers samples of the ni sulfide layer from the yukon territory are highly enriched in re os and other pge with distinctly higher re 192os but similar pt re compared to the black shale host re os isotopic data of the black shale and the sulfide layer are approximately isochronous and the data plot close to reference isochrons which bracket the depositional age of the enclosing shales samples of the chinese sulfide layers are also highly enriched in re os and the other pge re 192os are lower than in the yukon sulfide layer re os isotopic data for the sulfide layers lie near a reference isochron with an age of 560 ma similar to the depositional age of the black shale host the osmium isotopic data suggest that re and pge enrichment of the brecciated sulfide layers in both the yukon territory and in southern china may have occurred near the time of sediment deposition or during early diagenesis during the middle to late devonian and early cambrian respectively

spatial scale partitioning of in situ turbulent flow data over a pebble cluster in a gravel bed river 1 spatial structures within turbulent flow data were investigated through the use of a new multivariate variation partitioning analysis technique involving principal coordinates of neighbor matrices pcnm which is a form of distance based eigenvector maps dbem the analysis revealed a significant 0 01 spatial dependence 58 for the mean and turbulent flow variables the flow variables were obtained from instantaneous two dimensional velocities collected in situ along a streamwise section that crosses over a pebble cluster in a gravel bed river using the orthogonal property of the pcnm variables the explained variation was partitioned over four significant 0 01 spatial scales very large vl 17 large l 24 medium m 6 and fine f 2 nearly 75 of the variance of the main turbulent flow indicators such as the root mean square of the streamwise and vertical velocity components and the mean uv component reynolds shear stress was explained by the vl and l scale pcnm submodels which have streamwise and vertical length scales of the order of x 5 3h 2 6h and y 1 0h 0 5h where h is the flow depth respectively through a multivariate mapping procedure clear spatial patterns within the explained flow variables emerge around the cluster where the flow separation zone seems to play a significant role at a range of scales as well intervariable correlations at each spatial scale obtained through eigenvector scatterplots show intricate relationships between the flow variables the interdependence of the reynolds shear stress and the u component turbulent energy is much stronger at the vl scale than at the l and m scales the application of pcnm analysis on the turbulent flow field shows the power of the technique to resolve the relevant spatial scales and patterns and demonstrates its potential use in a variety of water resources studies

rhenium osmium evidence for regional mineralization in southwestern north america more than 40 base metal porphyry ore deposits in southwestern north america are associated with the laramide orogeny about 90 million to 50 million years ago rhenium osmium dates on molybdenite a rhenium enriched sulfide common in many of the deposits reveal that in individual deposits mineralization occurs near the final stages of magmatic activity irrespective of the time of inception magnitude or duration of magmatism deposits that differ widely in location and in the extent and timing of magmatism have nearly identical ages for mineralization rhenium osmium ages suggest that mineralization occurred during two distinct intervals from about 74 million to 70 million years ago and from 60 million to 55 million years ago most deposits that formed in the oldest interval are within the older precambrian basement of northwestern arizona whereas the younger deposits are restricted to the younger precambrian basement in southern arizona and northern mexico synchronous widespread mineralization indicates that similar crust mantle interaction occurred on a regional scale for ore deposits once thought to be the product of localized processes

re os isotopic and trace element compositions of pyrite and origin of the cretaceous jinchang porphyry cu au deposit heilongjiang province ne china abstract the jinchang cu au deposit in northeast china contains more than 76 tons of au and 4683 tons of cu with average ore grades of 11 34 g t au and 1 44 cu the deposit is typical of porphyry types and consists of gold orebodies mainly hosted in a 113 ma granitic porphyry and breccia pipes within the porphyry intrusion mineralization is closely associated with early potassic alteration and late phyllic alteration pyrite is the main au bearing mineral and contains 1 48 18 9 ppb re and 11 4 38 ppt common os extremely low common os concentrations and high re os ratios are indicative of derivation of ore forming materials from the crust low re in pyrite from the jinchang deposit may indicate a mixing source of mantle and crust or a crustal source five re os isotopic analyses yield a model 1 isochron age of 114 22 ma 2 mswd 0 15 similar to the age of the host porphyry pyrite contains detectable co ni cu zn as ag au sb pb and bi pyrite has co ni ratios similar to that of volcanogenic and hydrothermal sulfide deposits indicating a magmatic hydrothermal origin and has au and as contents similar to that of porphyry epithermal systems pyrite grains from potassic and phyllic alteration stages have different trace element contents reflecting the evolution of ore forming fluids from magmatic dominated to magmatic mixed with meteoric water in combination with regional geology our new results are suggestive of origin of the jinchang cu au deposit from contemporary intrusions of granitic porphyries related to the early cretaceous subduction of the paleo pacific plate

mean and turbulent velocity fields near rigid and flexible plants and the implications for deposition 1 the transport of fine sediment and organic matter plays an important role in the nutrient dynamics of shallow aquatic systems and the fate of these particles is closely linked to vegetation we describe the mean and turbulent flow near circular patches of synthetic vegetation and examine how the spatial distribution of flow is connected to the spatial distribution of suspended sediment deposition patches of rigid emergent and flexible submerged vegetation were considered with two different stem densities for the rigid emergent vegetation flow adjustment was primarily two dimensional with flow deflected in the horizontal plane horizontal shear layers produced a von karman vortex street flow through the patch shifted the vortex street downstream resulting in a region directly downstream of the patch in which both the mean and turbulent velocities were diminished net deposition was enhanced within this region in contrast for the flexible submerged vegetation flow adjustment was three dimensional with shear layers formed in the vertical and horizontal planes because of strong vertical circulation turbulent kinetic energy was elevated directly downstream of the patch consistent with this deposition was not enhanced at any point in the wake this comparison suggests that morphological feedbacks differ between submerged and emergent vegetation further enhanced deposition occurred only in regions where both turbulent and mean velocities were reduced relative to the open channel reduced deposition indicating enhanced resuspension occurred in regions of high turbulence kinetic energy regardless of local mean velocity these observations highlight the importance of turbulence in controlling deposition

sea bed noises reveal role of turbulent bursting phenomenon in sediment transport by tidal currents in many engineering and sedimentological applications it is usual to relate sediment movement to the time averaged bed shear stress however the shear stress exerted on the sea bed by tidal currents is intermittent in nature due to the turbulent bursting phenomenon1 2 sediment movement at the sea bed also occurs in bursts3 4 however attempts to link these two processes have failed because of the poor temporal resolution of existing sediment transport measurement techniques recent experimental advances now make this possible and we describe here the first detailed observations of sediment movement and fluid turbulence in tidal currents flowing over sandy gravels these results show that high stress values are a necessary but not sufficient condition for bed load sediment movement and that form drag on individual particles may have greater dynamical significance than the stress this work also suggests that it may now be possible to describe sediment movement at a level which is deterministic in terms of the turbulence and at very much shorter timescales than have been used previously

application of the 187re 187os system to black shale geochronometry the decay of 187re to 187os provides a tool for determining depositional ages of black shales re and os concentrations and os isotopic compositions of whole rock samples of the bakken shale a mississippian devonian boundary black shale yield a whole rock isochron with an age of 354 49 ma this age is in agreement with the accepted age of the bakken shale 360 ma the initial 187os186os ratio of the isochron is 6 2 3 3 this value is indistinguishable from the 187os186os ratios observed in modern black sea sediments the concentration of common os in bakken shale samples is strongly correlated with total nitrogen indicating that a large fraction of the os in these samples is associated with a hydrogenous component which overwhelms any os supplied to the sediment in association with detrital material or cosmic dust the dominance of the hydrogenous component imparts a relatively homogeneous initial 187os186os ratio to the sediment at the time of deposition the degree of scatter about the isochron exceeds the degree of scatter expected from either analytical error or from the estimated degree of initial isotopic heterogeneity the pattern of scatter is consistent with postdepositional mobilization of re and or os on a small spatial scale we suggest that this mobilization may be a consequence of petroleum formation and migration in the bakken shale

zircon u pb and molybdenite re os geochronology and geochemistry of jinchang porphyry gold copper deposit ne china two phase mineralization and the tectonic setting abstract whether multiple mineralization styles in porphyry deposits are the result of one or multiple pulses of magmatism is unknown in this paper we present new age and geochemical data on the jinchang porphyry gold copper au cu deposit an important deposit in ne china and in the eastern central asian orogenic belt caob field geological study suggests that both the mineralization and ore causative magmatism at jinchang are multiphase la icp ms zircon u pb dating of the monzogranite ore host yielded 197 1 ma which is considerably older than the ore causative monzonite 115 3 ma and granodiorite 107 2 ma molybdenite re os dating on the breccia pipe hosted au cu ores yielded a well defined isochron age of 114 3 ma coeval to the monzonite emplacement the au cu mineralization was followed by another phase of crypto explosive breccia pipe hosted disseminated vein type au mineralization this au only mineralization phase was auriferous pyrite re os dated to be 103 101 ma coeval to the granodiorite emplacement geochemically the monzonite and granodiorite are enriched in liles and lrees but depleted in hfses and hrees the ore causative rocks are i type and display continental arc geochemical affinities we suggest that the monzonite and granodiorite were generated in an intracontinental extensional setting probably caused by the early cretaceous subduction roll back of the paleo pacific plate

crustal affinities of metallogenesis in the american southwest the source of metals in many lands of ores and ore deposit styles remains uncertain notwithstanding more than a century of field studies scientific advances in concepts and enhancement of analytical capability however numerous geologic research efforts that have addressed many relevant themes in southern arizona have resulted in different kinds of data supporting and consistent with the interpretation of significant association of some ore metals of this region with cratonic crust these themes range in scale from studies of regional geology geophysical interpretations and precious metal production through petrology to trace element and isotope geochemistry the notion of a crustal source for metals contrasts with many long standing ideas of direct mantle sources for this metal province or more recently direct derivation of metals from subducted materials a hundred years of recorded silver and gold production reveal a two fold separation of mining districts in arizona and new mexico on the basis of ranges of produced ag au ratio that correspond in turn with a separation of two distinct geologic domains of the southern cordilleran metal province the produced ag au ratio in districts of different ages ore styles tectonic setting and metal habit are not affected by deposit style or ore control or igneous rock type or vertical zoning and weathering studies of the isotopes and trace element chemistry of related igneous rocks reveal that ore related intrusions have a significant crustal progenitor studies of pb and os isotopes have discovered strong signals of crustal parentage in ore minerals the regional geology metallization history production and chemical and isotopic data strongly support a hypothesis of crustal sources of some of the metal in this large and complex province

re os isotopic constraints on the genesis and evolution of the dergamish and ivanovka cu co au massive sulphide deposits south urals russia abstract rhenium and osmium elemental and isotopic data have been obtained for the two mafic ultramafic hosted volcanogenic massive sulphide vms deposits of dergamish and ivanovka from the south urals the associated ophiolitic blocks belong to the main uralian fault muf melange zone considered to represent obducted early palaeozoic oceanic crust despite their close geographical proximity the two ore bodies are morphologically mineralogically and isotopically quite different sulphides from ivanovka possess higher ni and os and lower re and cu relative to those from dergamish the re and os isotope data for dergamish define a best fit line corresponding to a late devonian age of 366 2 ma 2 with an mswd of 4 6 this age is some 40 my younger than the inferred silurian crystallisation age of the associated mafic ultramafic rocks but in good agreement with the previously published rb sr and ar ar ages of 360 380 ma corresponding to the high pressure metamorphic age of the adjacent maksyutov metamorphic complex these data suggest that re os systematics of the dergamish sulphide deposit were reset either by diffusion or recrystallisation during high pressure metamorphism or subsequent cooling the preservation of unradiogenic os isotopic ratios in some of the ivanovka samples and the near chondritic initial os isotopic composition obtained for the dergamish samples indicates that most of the os in the massive sulphides was ultimately derived from the mantle the corresponding tectonic setting equates to an area with submarine high level mantle rocks in contrast sulphides from ivanovka have experienced continued re equilibration and have been modified by post depositional processes at least some of which occurred relatively recently

the timing origin and t fo2 crystallization conditions of long lived magmatism at the yangla copper deposit sanjiang tethyan orogenic belt implications for post collisional magmatic hydrothermal ore formation abstract an integrated study involving zircon geochronology hf isotopic characteristics and trace elements combined with detailed field investigation was carried out for the felsic magmatic system in the yangla skarn copper deposit area in the sanjiang orogenic belt southwestern china the intrusive units are composed of syn mineralized dioritic enclaves granodiorite quartz monzonite porphyry 238 230 ma and granite stocks and monzogranite dikes 223 ma bracketing a time span of ca 15 myr the uniform hf isotope characteristics during an 15 myr period suggest a primary control of the isotopic signature by a stable long lived hot reservoir in the deep lithosphere the occurrence of mafic enclaves and the identical intermediate initial ehf values 5 9 to 1 7 of granodiorite granite and monzogranite suggest that the felsic magmatic system was produced by remelting of neoproterozoic lower crustal rocks that mixed with minor amounts of mantle derived melts application of comprehensive indices of zircons such as th u zr hf t ti in zircon and ce nd implies that 1 mafic melt injected into felsic magma during the early stage from which the granodiorite and dioritic enclaves formed 2 progressive evolution from granodiorite to quartz monzonite porphyry with addition of crustal components as revealed by the positive correlation between ehf and th u 3 the incorporation of the crustal component into the residual magma from which quartz monzonite porphyry formed reduced the f o2 of the mineralized and barren quartz monzonite porphyry and settled much of dense sulfides out at depth and 4 another discrete reduced magma pulse from which the granite and monzogranite dikes crystallized at slightly higher ti in zircon model temperatures suggesting a slightly more reduced condition of the hidden intrusive portion of magma chamber in general the magmatic system is interpreted to be related to post collisional lithospheric extension after slab break off the cu s and water of the felsic magmas were mainly derived from the recycling of neoproterozoic hydrous arc lower crustal rocks triggered by asthenospheric upwelling

examining the physical components of boundary shear stress for water worked gravel deposits it is argued in this commentary that in order to understand better the physical mechanisms that generate boundary shear stress over water worked gravel beds flow velocity data should be re evaluated by spatial averaging the reynolds equations to produce time and space averaged double averaged momentum equations a series of laboratory experiments were conducted in which the flow velocities were measured using a piv system over two water worked gravel deposits combined with detailed data on the bed surface topography and vertical porosity the physical components of shear stress were obtained this enabled the various momentum transfer mechanisms present above within and at the interface of a porous fluvial deposit to be quantified this included the examination of the relevant contributions of temporal and spatial fluctuations in velocity and surface drag to the overall momentum transfer it is demonstrated that double averaging represents a logical framework for assessing the fluid forces responsible for sediment entrainment and for investigating intragravel flow and sediment water interface exchange mechanisms within the roughness layer in water worked gravel deposits by considering the physical components of shear stress and their relative sizes it was possible to provide a physically based explanation for existing observations of enhanced mobility of gravel sand mixtures and the transfer of solutes into porous gravel deposits this analysis reveals the importance of obtaining co located high quality spatial data on the flow field and bed surface topography in order to gain a physical understanding of the mechanisms which generate boundary shear stress copyright 2010 john wiley sons ltd

long term in situ calculations of kinetic energy and reynolds stress in a deep sea boundary layer long term measurements of reynolds stress and kinetic energy are necessary to characterize the bottom boundary layer during storms which transport sediment in the high energy benthic boundary layer experiment area on the nova scotia rise the benthic acoustic stress sensor current meter system employed an on board microcomputer to process 2 hz velocity vector data into 20 min averages of velocity vectors and the turbulent reynolds stress tensor the data indicate a bottom boundary layer which is usually transitional with bottom roughness scaling between viscous z0 v 9u and rough z0 ks 30 during the periods of transitional flow the logarithmic layer was not a useful indicator of boundary stress direct stress and energy measurements showed that the stress was much less than that indicated by the slope of the transitional mean logarithmic velocity profile several westward high velocity events which were modulated by a significant tidal component were recorded it appears from this data set that the mean westward flow must be accompanied by a train of internal tidal waves to achieve the velocities necessary to be the sediment transport events identified as benthic storms