zircon xenocrysts from the kambalda volcanics age constraints and direct evidence for older continental crust below the kambalda norseman greenstones abstract the hangingwall basalt at kambalda western australia contains zircons that have been shown by ion microprobe analyses to have very high u and th contents and a wide variety of crystallization ages nearly all of these zircons certainly are xenocrysts a few might relate to intrusive veinlets the age of the youngest xenocrysts 2693 50ma 2 shows that the eruptive age of the basalt cannot exceed 2743 ma this confirms that the apparent sm nd isochron giving 3200 ma 1 2 for kambalda mafic and ultramafic rocks is a mixing line 2 between unrelated components enriched and depleted in light rare earth elements mixing probably occurred at depth by erosion of 3200 3500 ma old felsic crust from the walls of the hwb conduits the zircon xenocryst ages are the first direct evidence for the presence of very old felsic crust in the eastern yilgarn block the latter implies that the kalgoorlie norseman greenstone sequences were formed in a continental rather than an oceanic environment

ocean bottom profiling with ambient noise a model for the passive fathometer a model is presented for the complete passive fathometer response to ocean surface noise interfering discrete noise sources and locally uncorrelated noise in an ideal waveguide the leading order term of the ocean surface noise contribution produces the cross correlation of vertical multipaths and yields the depth of sub bottom reflectors discrete noise incident on the array via multipaths give multiple peaks in the fathometer response these peaks may obscure the sub bottom reflections but can be attenuated with use of minimum variance distortionless response mvdr steering vectors the seabed critical angle introduces discontinuities in the spatial distribution of distant surface noise and may introduce spurious peaks in the passive fathometer response these peaks can be attenuated by beamforming within a bandwidth limited by the array geometry and critical angle

the golden mile kalgoorlie a giant gold deposit localized in ductile shear zones by structurally induced infiltration of an auriferous metamorphic fluid mesoscopic and microscopic analysis of the structurally controlled gold mineralization of the golden mile kalgoorlie has demonstrated that the mineralogically simple gold pyrite mineralization style 70 of production is restricted to an anastomosing system of narrow high strain zones ductile shear zones and to related tension fractures in the intervening unstrained rock virtually all ductile shear zone lode structures occur in the golden mile dolerite because it was essentially mechanically isotropic prior to deformation it is proposed that during the near upright regional folding event numerous ductile shear zones were established in an approximately axial planar relationship to the folds with synchronous conjugate shear zones developed at low angles to this direction a dynamic analysis shows that the tensional cross lodes can be related geometrically to the three ductile shear zones golden mile style mineralization is syntectonic and was not deposited posttectonically in structurally prepared sites microtextural analysis demonstrates that minerals associated with gold emplacement are strongly modified during strain within the ductile shear zones by ductile deformation dominated by mass transfer processes in particular there is abundant evidence of crack seal type microfracturing within and marginal to grains and in microscopic transgranular sites this deformation style contributed prominently to the bulk plastic flow of the shear zones it is proposed that high fluid pressure gradients were established at each crack seal cycle leading to much enhanced permeability and to considerable focusing of fluid flow through the narrow foliated zones this structurally induced infiltration mechanism allowed the ore fluid to pervade the deforming zones and also controlled the straining process by moving dissolved mineral components from highly stressed contacts to sites of deposition thus the mineralization was introduced during the ductile phase of shear zone evolution and though mesoscopic veins are present in the ductile shear zones they are not a necessary part of the gold emplacement event the majority of veins formed late in the tectonic history gold emplacement in the ductile shear zones was controlled by microscopic deformation processes and ductile shear zones are good exploration targets even in the absence of macro to mesoscopic dilation sites

rheological stratification of the lithosphere abstract the rheology of the lithosphere is estimated on the basis of pore pressure dependent frictional failure in the brittle regime and power law steady state creep in the ductile regime different petrological models of the continental and oceanic lithosphere combined with different geotherms and thicknesses are used to generate models covering a variety of geodynamic situations results show that the depth dependence of lithospheric rheology varies with the tectonic province and that in many instances the continental lithosphere has one at the bottom of the crust or two the previous one plus another at mid crustal levels soft ductile layers sandwiched between brittle layers the depth distribution of geophysical parameters seismicity seismic wave velocity and electrical conductivity matches the theological predictions well the lithospheric rheological profiles are used to analyze observed variations in the structural style of deformed continental margin and oceanic terranes in the southeastern canadian cordillera the large scale characteristics of the system show a satisfactory agreement with the inferred rheological structure sub horizontal decollements should be the rule rather than the exception where the lithospheric rheology is strongly stratified

target detection and location with ambient noise by placing a vertical array in an ambient noise field and forming an upward and a downward beam one obtains two time series which can be cross correlated to reveal a subbottom profile of the seabed siderius et al j acoust soc am 120 1315 1323 2006 here the cross correlation approach is applied to the location in range and bearing of a point target an experiment was designed using floats and weights mounted and dismounted on the same cable as the vertical array careful measurements were made of the location of all likely floats ballast weights array terminations and so on after suitable coherent averaging peaks were seen at delays correlation offsets agreeing with the reflector positions and were shown to be absent when reflectors were removed a trivial extension of the theory developed in harrison and siderius j acoust soc am 123 1282 1296 2008 is used to explain the rough amplitudes of the reflections the approach differs from acoustic daylight principally in having a

roughness at the base of the seismogenic zone contributing factors the cutout depth of microseismic activity in continental fault zones appears to correspond to the onset of greenschist metamorphic conditions at about 300 c it can generally be modeled as the transition from frictional to quasi plastic behavior in quartzofeldspathic crust shear resistance increases with depth through the frictional regime to peak at the transition beneath which it falls off exponentially with increasing temperature larger earthquake ruptures ml 5 5 nucleate around this transition depth where the highest concentrations of strain energy may accumulate varying depth and amplitude of the peak shear resistance along strike induce fluctuations in strain energy concentration at the base of the seismogenic zone factors affecting the depth of the transition include crustal composition geometry and mode of faulting fluid pressure levels in the frictional regime and water content in the quasi plastic regime quasi plastic strain rate and geothermal gradient evaluation of their relative importance is complicated because several are interdependent however compositional change may cause abrupt irregularities in seismogenic depth and peak shear resistance while regional variations in heat flow look to be particularly effective in creating long wavelength heterogeneities in strain energy concentration affecting faulting style

archean gold bearing quartz veins at the sigma mine abitibi greenstone belt quebec part i geologic relations and formation of the vein system the sigma deposit consists of an archean gold bearing vein system in metavolcanic rocks intruded by an irregular body of porphyritic diorite both affected by regional deformation and in turn cut by younger undeformed feldspar porphyry dikes the veins cut all rock types and are composed chiefly of quartz and tourmaline with minor amounts of carbonates pyrite chlorite scheelite and free gold they were emplaced during or after a greenschist facies metamorphism postdating the intrusion of feldspar porphyry dikes the veins were not significantly affected by any subsequent metamorphism or tectonism two principal types of veins occur in the mine subvertical veins and subhorizontal veins they are contemporaneous and cogenetic subvertical veins occur within steeply dipping east west trending ductile shear zones along which reverse subvertical displacements have taken place the veins occupy openings created by overriding of undulations and irregularities of foliation and slip planes during progressive shearing movements within the shears subhorizontal veins occupy extensional fractures which developed between ductile shear zones preferentially in the more competent host rocks these veins were formed by one or several episodes of open space filling geologic relations indicate that the mineralized veins were emplaced progressively in a dynamic tectonic environment during and shortly after the formation of ductile shear zones a structural analysis has shown that the ductile shear zones and the two vein types can be related to a single strain ellipsoid of the following orientation the z axis trending north south and horizontal the y axis plunging 10 degrees west and the x axis plunging 80 degrees east the deformation responsible for the generation of ductile shear zones and emplacement of the veins is ascribed to a late north south trending compression postdating regional deformation

incompatible element enrichment in archean basalts a consequence of contamination by older sialic crust rather than mantle heterogeneity high abundances of incompatible elements in mgo rich archean basalts from western australia which were thought to have been derived from an enriched mantle source are probably the result of contamination of primitive magmas by small amounts of older sialic crust because these lavas represent some of the more extreme cases of enrichment in incompatible elements observed in archean basalts it may be possible to explain much of the trace element variation previously ascribed to a heterogenous archean mantle by variable crustal contamination of mantle derived magmas recent calculations of thermal erosion rates predict that high temperature high mgo magmas abundant in the archean are most susceptible to contamination therefore a cautious reappraisal of isotopic and trace element data from archean greenstone belts is required before the real extent of archean mantle heterogeneity can be established

particle filtering for passive fathometer tracking seabed interface depths and fathometer amplitudes are tracked for an unknown and changing number of sub bottom reflectors this is achieved by incorporating conventional and adaptive fathometer processors into sequential monte carlo methods for a moving vertical line array sediment layering information and time varying fathometer response amplitudes are tracked by using a multiple model particle filter with an uncertain number of reflectors results are compared to a classical particle filter where the number of reflectors is considered to be known reflector tracking is demonstrated for both conventional and adaptive processing applied to the drifting array data from the boundary 2003 experiment the layering information is successfully tracked by the multiple model particle filter even for noisy fathometer outputs

a passive fathometer technique for imaging seabed layering using ambient noise a passive acoustics method is presented that uses the ocean ambient noise field to determine water depth and seabed sub bottom layering correlating the noise field measured by two sensors one can recover a function that closely resembles the two point green s function representing the impulse response between the two sensors here a technique is described that is based on noise correlations and produces what is effectively a passive fathometer that can also be used to identify sub bottom layers in principle just one or two hydrophones are needed given enough averaging time however by combining the cross correlations of all hydrophone pairs in a vertical array a stronger signature can be obtained and this greatly reduces averaging time with a moving e g drifting vertical array the resulting algorithm yields both a map of the bottom depth passive fathometer and the locations of significant reflectors in the ocean sub bottom in this paper the technique is described and illustrated using numer

effects of sea surface conditions on passive fathometry and bottom characterization recently a method has been developed that exploits the correlation properties of the ocean s ambient noise to measure water depth a passive fathometer and seabed layering m siderius et al j acoust soc am 120 1315 1323 2006 this processing is based on the cross correlation between the surface noise and the echo return from the seabed to quantitatively study the dependency between processing and environmental factors such as wind speed measurements were made using a fixed hydrophone array while simultaneously characterizing the environment the measurements were made in 2006 in the shallow waters 25 m approximately 75 km off the coast of savannah ga a navy tower about 100 m from the array was used to measure wind speed and to observe the sea surface using a video camera data were collected in various environmental conditions with wind speeds ranging from 5 to 21 m s and wave heights of 1 3 4 m the data are analyzed to quantify the dependency of passive fathometer results on wind speeds wave conditions and averaging times one result shows that the seabed reflection is detectable even in the lowest wind conditions further a technique is developed to remove the environmental dependency so that the returns estimate seabed impedance doi 10 1121 1 3216915

a model for the spatial coherence of arbitrarily directive noise in the depth stratified ocean though referred to as noise the ambient ocean soundscape carries valuable information about the physical ocean environment to study this information kuperman and ingenito introduced a model for spatial coherence in a depth stratified ocean arising from the vertically directive diffuse acoustic noise produced by bubbles distributed throughout the surface here the model is adapted to incorporate horizontal directivity as well making it possible to include additional noise contributions from directive features such as storms biologics shipping and wave breaking as an analytic approach the model can serve as a computationally light complement to existing methods

fluid participation in deep fault zones evidence from geological geochemical and 18o 16o relations fluid incursion into fault zones and their deeper level counterparts brittle ductile shear zones is examined in a number of different crustal environments at the grenville front translation was accommodated along two mylonite zones and an associated boundary fault the high mz ii and low temperature mz i mylonite zones formed at 580 to 640 c and 430 to 490 c respectively in the presence of fluids of metamorphic orgin indigenous to the immediate rocks a population of posttectonic quartz veins occupying brittle fractures were precipitated from fluids with extremely negative 18o at 200 to 300 c the water may have been derived from downwards penetration into fault zones of low 18o precipitation on a mountain range induced by continental collision with uplift accommodated at deep levels by the mylonite zones coupled with rebound on the boundary faults at lagoa real brazil archaean gneisses overlie proterozoic sediments along thrust surfaces and contain brittle ductile shear zones locally occupied by uranium deposits following deformation at 500 to 540 c in the presence of metamorphic fluids and under conditions of low water to rock ratio shear zones underwent local intense oxidation and desilicification all minerals undergo a shift of 10 indicating discharge of meteoric water recharged formation brines in the underlying proterozoic sediments up through the archaean gneisses during overthrusting about 1000 km3 of solutions passed through these structures at yellow knife a series of large scale shear zones developed by brittle ductile mechanisms involving volume dilation with migration of 5 wt volatiles into the shear zone from surrounding metabasalts this early deformation involved no departures in redox state or whole rock 18o from background states of fe2 fe 0 72 and 7 to 7 5 respectively attesting to conditions of low water rock shear zones subsequently acted as high permeability conduits for pulsed discharge of 9 km3 of reduced metamorphic hydrothermal fluids at 360 450 c the west bay fault a late major transcurrent structure contains massive bull quartz that grew at 200 300 c from fluids of 2 to 6 possibly formation brines in general flow regimes in these fault and shear zones follow a sequence from conditions of high temperature and pressure with locally derived fluids at low water to rock ratios during initiation of the structures to high fluxes of reduced formation or metamorphic fluids along conduits as the structures propagate and intersect hydrothermal reservoirs later in the tectonic evolution and at shallower crustal levels there was incursion of oxidizing fluids from near surface reservoirs into the faults

bottom profiling by correlating beam steered noise sequences it has already been established that by cross correlating ambient noise time series received on the upward and downward steered beams of a drifting vertical array one can obtain a subbottom layer profile strictly the time differential of the cross correlation is the impulse response of the seabed here it is shown theoretically and by simulation that completely uncorrelated surface noise results in a layer profile with predictable amplitudes proportional to those of an equivalent echo sounder at the same depth as the array the phenomenon is simulated by representing the sound sources as multiple random time sequences emitted from random locations in a horizontal plane above a vertical array and then accounting for the travel times of the direct and bottom reflected paths a well defined correlation spike is seen at the depth corresponding to the bottom reflection despite the fact that the sound sources contain no structure whatsoever the effects of using simultaneously steered upward and downward coni

archean wrench fault tectonics and structural evolution of the blake river group abitibi belt quebec structural analysis of the blake river group volcanic rocks in the rouyn noranda region shows the formations to be distributed largely in z shapes resulting from the interference of two early fold systems oriented west northwest east southeast and east west respectively the first of these two fold systems is probably related to the shortening associated with left lateral movement along the two major fractures in the region namely the porcupine destor and larder lake cadillac faults the second system appears to be the result of north south compression perpendicular to the two major fractures the two major faults the first system of early folding the normal and reverse faults and the minor dextral and sinistral strike slip faults that have been observed in the blake river group rocks can all be integrated into one tectonic system that of wrench fault tectonics the orientations of the principal structures recognized in the abitibi belt major shear zones folding and faulting suggest that the d

crustal scale shear zones and their significance to archaean gold mineralization in western australia many large archaean epigenetic gold deposits show a broad spatial relationship to regional lineaments in greenstone belts although in detail they are sited in subsidiary brittle ductile fault structures fluids originating from a deep source follow a complex path and re equilibrate with different lithologies and with metamorphic fluid during migration to higher crustal levels temperature and pressure conditions at or below the amphibolite greenschist metamorphic boundary where most gold deposits are located favour the establishment of brittle ductile and brittle subsidiary structures the preferred structural setting of gold deposits physical gradients between the regional ductile structures and more brittle subsidiary structures ensure transient strongly localized fluid flow into the latter where lower temperatures and suitable host rocks with high fe fe mg ratios favour gold deposition the multi source origin and continuous re equilibration of the fluid with crustal rock which includes granitoid and greenstone belt lithologies of different ages is reflected in the diverse isotopic and geochemical signature of the gold deposits

frequency based noise coherence function extension and application to passive bottom loss estimation accurate modeling of acoustic propagation in the ocean waveguide is important to sonar performance prediction particularly in shallow waters a crucial contribution to the total transmission loss is the bottom refection loss which can be estimated passively by beamforming the natural surface noise acoustic field recorded by a vertical line array of hydrophones however the performance in this task of arrays below 2 m of length is problematic for frequencies below 10 khz it is shown in this paper that when the data are free of interference from sources other than wind and wave surface noise data from a shorter array can be used to approximate the coherence function of a longer array this improves the angular resolution of the estimated bottom loss often making use of data at frequencies above the array design frequency application to simulated and experimental data shows that the technique rigorously justified for a halfspace bottom is effective also on more complex bottom types dispensing with

passive fathometer reflector identification with phase shift modeling in passive fathometer processing the presence of wavelets in the estimate of the medium s green s function corresponds to the location of reflectors in the seabed amplitudes are related to seabed properties bayesian methods have been successful in identifying reflectors that define layer interfaces further work however revealed that phase shifts are occasionally present in the wavelets and hinder accurate layer identification for some reflectors with a gibbs sampler that computes probability densities of reflector depths strengths of the reflections and wavelet phase shifts the significance of phase shift modeling in successful estimation of reflectors and their strengths is demonstrated

craton scale distribution of archean greenstone gold deposits predictive capacity of the metamorphic model genetic models should not only attempt to explain features of archean gold mineralization on the scale of mines or districts but should also explain its marked spatial and temporal heterogeneity in greenstone belts the application of genetic models developed with such a philosophy can have predictive capacity in gold exploration the metamorphic model one of a number of current genetic models for archean gold deposits involves generation of auriferous h 2 o co 2 fluids by devolatilization of the stratigraphically lowermost greenstones during metamorphism and broadly synchronous synkinematic granitoid intrusion crustal scale fault shear systems are required to induce channeled fluid flow and to focus ore fluids toward suitable host rocks and structural sites declining temperature below the amphibolite greenschist transition combined with sulfidation of fe rich host rocks is a particularly efficient au depositing mechanism the model suggests that the major controlling factors in declining order of importance are 1 high temperature low pressure generally low strain metamorphic regimes 2 crustal scale fault systems 3 unaltered fe rich rocks tholeiites banded iron formation at a suitable stratigraphic metamorphic level and 4 abundant au enriched komatiites and s rich sediments in source regions the low pressure metamorphic conditions combined with the occurrence of elongate high strain zones in most if not all generally low strain greenstone belts may explain the ubiquitous occurrence of gold deposits in archean terranes all four favorable parameters appear to act in concert to produce the largest gold deposits and most abundant gold mineralization in 2 7 or 0 1 b y old rift phase greenstone belts interpreted to have formed under conditions of high crustal extension and extensive crustal thinning i e with predicted high geothermal gradients high fault density limited synvolcanic alteration and abundant komatiites and sulfidic sediment horizons more widespread commonly older platform phase greenstone belts which formed under conditions of lesser crustal extension and thinning are less mineralized as predicted by the metamorphic model the ability of the model to explain the regional distribution of known archean gold deposits lends credence to its predictive capacity for example 1 greenstone belts in any one craton can be broadly ranked in order of likely relative gold potential 2 the likelihood of discovery of large deposits in poorly exposed or poorly explored belts of known type can be estimated 3 areas with the highest potential can be defined in rift phase greenstone belts by the coincidence of critical parameters such as specific host rock sequences and metamorphic facies 4 prospective structural sites for gold mineralization can be postulated in platform phase greenstone belts affected by diapiric tectonics and 5 the possible spacing of large deposits can be estimated further the potential use of the model in exploration emphasizes serious gaps in our knowledge of parameters crucial to understanding greenstone belt metallogeny including alteration patterns metamorphic p t paths and regional scale structural regimes

fluid rock interaction in some shear zones from the pyrenees mylonites from shear zones cutting hercynian gneisses in the central pyrenees have been studied in thin section and using the electron microprobe the shear zones contain retrogressive greenschist facies assemblages implying introduction of an aqueous fluid during deformation in the zones textural evidence suggests that fluid rock interaction occurred throughout the active life of the shear zones whole rock chemical changes during deformation are documented in a variety of mylonitic lithologies and retrogressed country rocks the overall effect was to reduce chemical differences between lithologies activity diagrams show that this would be expected if a hydrous fluid was circulating between different lithologies during deformation in most cases fluid rock ratios were relatively small resulting in gradual chemical changes and repeated recrystallization open system behaviour with reduction in the number of phases is seen in some granite mylonites suggesting focusing of fluid movement in parts of the shear zones continual fluid rock interaction may have led to reaction enhanced ductility in the shear zones over a long period of time the source of fluid is uncertain but may be related to underthrusting of material beneath the area investigated

early proterozoic ore deposits and tectonics of the birimian orogenic belt west africa abstract the early proterozoic of the west african craton comprises a series of volcanic troughs and sedimentary basins the birimian with granitic terranes accreted on archean nuclei in the man and reguibat shields studies of the birimian of the man shield indicate a model of polycyclic evolution with a major collision event d 1 2 1 ga thrusting part of the proterozoic terrane over the archean before individualization of numerous volcanic troughs and clastic infill basins the proposed evolution for the birimian orogenic belt comprises 1 deposition of the sedimentary lower birimian b1 with minor tholeiitic volcano sedimentary intercalations containing chert and or mn formations and with most of the detritus being derived from early proterozoic sources apart from contamination near the proterozoic archean contact 2 pre b2 crustal thickening related to d 1 thrusting 3 formation over about 40 ma of the upper birimian b2 with numerous volcanic troughs of different composition tholeiitic and rare komatiitic bimodal tholeiitic to calc alkaline volcano plutonic and tarkwaian clastic infill basins and 4 major transcurrent tectonics with sinistral d 2 and dextral d 3 strike slip faults such a tectonic evolution from a collision d 1 phase to a transcurrent d 2 d 3 phase is typical of collision belts and in the present case the evolution of the birimian orogenic belt can be extended into guyana the metallogenic history of the birimian shows a three phase evolution coinciding with the orogenic evolution and extends over almost 150 ma from the perkoa massive zn ag sulfides 2 12 ga with a clear mantle affinity to the latemesothermal au quartz veins 2 ga with according to lead isotopes a high crustal participation the economic mineralization of belt thus consists of 1 1 pre orogenic pre d 1 deposits related to early extension zones this was diverse with stratiform au tourmalinite type 1 au loulo in mali dorlin in guyana stratiform fe cu faleme in senegal and mn nsuta in ghana tambao in burkina faso and a single massive zn ag sulfide deposit perkoa in burkina faso associated with regional volcanosedimentary variably tholeiitic stratigraphic marker beds 2 2 syn orogenic post d 1 to syn d 2 d 3 deposits with disseminated au sulfides type 2 au yaoure in the ivory coast in extensional zones of the b2 followed by auriferous paleoplacers type 3 au in b2 extensional zones tarkwaian banket conglomerate or syn d 2 transtensional zones debris flow of orapu in guyana 3 3 late orogenic post peak d 2 d 3 deposits with mesothermal au mineralization evolving from a disseminated gold bearing arsenopyrite and au quartz lode type type 4 au ashanti in ghana to a quartz vein type with free gold and cu pb zn ag bi paragenesis most of the gold in west africa comes from this phase finally the metallogeny of the birimian appears as rich in au and mn formations and poor in volcanogenic mineralization and bif it differs from the archean metallogeny of west africa and other regions through the presence of certain deposit types such as au stratiform tourmalinite gold bearing conglomerate with au and fe ti oxides but no uranium or sulfides and au arsenopyrite rich shear zone deposits that are very common in but not exclusive to the proterozoic and paleozoic

rheological controls on the geometry of deep faults and the tectonic delamination of the continental crust recent seismic reflection profiles indicate that the deep faults in the continental crust may decouple deep within the crust or at the moho in the contribution it is argued that the decoupling horizons were initially zones across which variations in flow strength occur due to mineralogical differences in the principal rock types these can result in the tectonic delamination of the crust and at the moho calculations reveal marked strength differences across the moho once initial delamination occurs weak planes of mylonite develop along such surfaces and are preferentially reactivated during any subsequent deformation it is postulated that during tectonism the continental crust 1 does not act at depth as a single rigid entity 2 should not be considered as being firmly attached to the upper mantle and 3 is capable of moving independantly of the upper mantle

archaean carbon reservoirs and their relevance to the fluid source for gold deposits it is commonly assumed1 2 that seawater derived carbon in altered volcanic rocks is the only major pre metamorphic carbon in carbonate reservoir in archaean greenstone belts thus carbonates from archaean gold deposits with stable isotope ratios too negative median 13c 3 to have been derived from such carbon 13c usually assumed to be near 0 have been interpreted as being derived from a local felsic magmatic source1 barley and groves3 however recognize two carbonate alteration styles that predate regional metamorphism and gold mineralization in the norseman wiluna greenstone belt of western australia evidence is summarized below these are seafloor alteration and fault controlled regional alteration which as shown below have completely different carbon isotope compositions the latter median 13c 4 8 implies a major juvenile carbon co2 flux from the mantle during greenstone belt evolution and is thus of fundamental importance in itself however here we show why the mere existence of two carbon in carbonate reservoirs and variation in carbon isotope ratios of carbonates between individual gold deposits in one area negate some of the fundamental assumptions used to support magmatic fluid models1

extracting coherent wave fronts from acoustic ambient noise in the ocean a method to obtain coherent acoustic wave fronts by measuring the space time correlation function of ocean noise between two hydrophones is experimentally demonstrated though the sources of ocean noise are uncorrelated the time averaged noise correlation function exhibits deterministic waveguide arrival structure embedded in the time domain green s function a theoretical approach is derived for both volume and surface noise sources shipping noise is also investigated and simulated results are presented in deep or shallow water configurations the data of opportunity used to demonstrate the extraction of wave fronts from ocean noise were taken from the synchronized vertical receive arrays used in the frame of the north pacific laboratory npal during time intervals when no source was transmitting

geology and alteration in the golden mile kalgoorlie the giant kalgoorlie gold deposit 1 200 metric tons au recovered is surrounded by a wide wall rock alteration halo 1 x 3 km this alteration primarily represents the selectively pervasive formation of carbonate chlorite and localized intense pyrite and muscovite alteration which all formed synchronously with gold mineralization the carbonate alteration halo is interpreted as epigenetic because of evidence that carbonate chlorite assemblages overprint regional metamorphic fabrics furthermore the geometry of the alteration zone boundaries is controlled by ductile shear zones formed during regional deformation and the geochemistry of all the alteration zones suggests that one fluid was responsible for all assemblages there is no evidence of intense premetamorphic carbonation in the kalgoorlie area kalgoorlie is situated in the highly auriferous eastern goldfields province of the yilgarn block within a narrow corridor rift zone that contains several large gold deposits regional metamorphism has produced upper greenschist facies assemblages but has retained original rock textures at kalgoorlie the most important gold host is the golden mile dolerite 80 of gold produced a differentiated tholeiitic sill intruded between a lower mafic ultramafic pile including the paringa basalt the next most important gold host and overlying felsic rocks and metasediments the kalgoorlie syncline is the dominant tectonic structure in the main gold producing area of the golden mile adjacent to this infold of metasediments the golden mile dolerite and paringa basalt are the site of a number of ductile shear zones which formed synchronously with the syncline these zones and the many smaller shear zones between them have provided fluid channelways throughout the golden mile and are the site of most economic gold mineralization three alteration zones have been mapped in the golden mile dolerite on the basis of the mineralogic siting of fe i e the chlorite carbonate and pyrite zones the additional actinolite zone representing the unaltered regional metamorphic mafic assemblage has been converted to chlorite zone assemblages throughout the mined areas of the golden mile the carbonate zone bleached dolerite can be traced for 2 km through the main mineralized parts of the golden mile and to the full depth of lake view mine the boundary between the chlorite and carbonate alteration zones is locally sharp and controlled by ductile shear zones but is generally strata bound and preferentially developed in the more fe rich parts of the dolerite the pyrite zone which includes all economically gold mineralized areas is the site of the strongest muscovite alteration and is most intense and continuous in ductile shear zones the chlorite zone chlorite calcite or ankerite forms from mild carbonation of actinolite zone assemblages the carbonate zone ankerite siderite is a more local expression of this carbonation even after extensive carbonate alteration relative major element abundances are little changed and the main added components are limited to co 2 s k and rb the pyrite zone i e the gold lodes has ankerite muscovite quartz albite pyrite and minor siderite bearing assemblages it represents significant addition of sulfur the three alteration zones not only reflect differing degrees of alteration intensity but are also strongly influenced by host rock fe mg and this ratio largely determines the stability of chlorite favored by low fe mg and thus the distribution of the carbonate zone favored by high fe mg progressive deformation within the shear zones reworked existing mineralization kalgoorlie fits a metamorphic replacement model of gold formation by auriferous metamorphic fluids interacting with fe rich host rocks its great size is a function of a very well developed fluid channelway system via ductile shear zones and later fault zones and the favorable chemical nature of the host rocks especially the golden mile dolerite the full width of carbonation chlorite and carbonate zones reflects overlapping alteration envelopes around the closely spaced fluid pathways the processes responsible for the formation of most of the gold at kalgoorlie were essentially similar to those at several other archean gold deposits but on a larger scale

a new shallow ocean technique for determining the critical angle of the seabed from the vertical directionality of the ambient noise in the water column in the absence of interference from local shipping the vertical directionality of ambient noise in the shallow ocean overlying a fast fluid sediment is a stable feature of the noise field it is controlled primarily by the bottom reflectivity which is a time invariant property of the channel the noise field shows a peak symmetrically placed around the horizontal whose angular width is 2 c where c is the critical grazing angle of the bottom by measuring the noise power distribution in the vertical c can be determined and hence the compressional sound speed in the bottom sediment deduced measurements of the vertical directionality of ambient noise in shallow water have been made at six sites around the coast of the united kingdom using specially designed vertical line array sonobuoys estimates for the critical grazing angle and the sound speed in the bottom have been derived from the noise data for all six areas similar data from independent seismic surveys are available for only one of these s

the genesis and tectonic control on archaean gold deposits of the western australian shield a metamorphic replacement model abstract gold deposits occur in greenstone belts world wide and contribute to anomalously high gold production from archaean terranes as in other cratons archaean gold mineralization of western australia represents a complex array of deposit styles despite this most deposits are clearly epigenetic and large deposits have a number of features in common including their strong structural controls distinctive wallrock alteration fe sulphide k mica albite ca mg fe carbonates consistent metal associations au ag as sb w b low base metals commonly fe rich host rocks great depth extension and lack of appreciable vertical zonation these shared characteristics combined with their ubiquitous occurrence indicate that archaean gold deposits had a common origin related to the tectonic evolution of greenstone belts auriferous hydrothermal systems were broadly synchronous with regional metamorphism and emplacement of synkinematic granitoids and felsic porphyry intrusions although these gold systems involved low salinity lowdensity reduced near neutral h 2 o co 2 fluids carrying gold as reduced sulphur complexes the origin of the fluids is equivocal most timing evidence and stable isotope data cannot distinguish metamorphic from magmatic granitoid or felsic porphyry orggins but the lack of consistent spatial relationships between specific volumetrically significant intrusive phases and large gold deposits in a number of cratons strongly favours metamorphic derivation of fluids the metamorphic replacement model for gold mineralization involves devolatilization of the lower portions of the greenstone pile with high geothermal gradients inhibiting significant melting co 2 possibly formed by the decarbonation of early alteration related to mantle degassing along crustal scale synbasinal fault zones auriferous fluids were channelled along greenstone scale faults in part developed during reactivation of crustal scale faults in a strike slip regime gold deposition occurred largely under greenschist facies conditions about 300 400 c 1 2 kb in response to decreasing gold solubility with declining temperature however a major control on gold deposition was fluid wallrock interaction many large deposits formed by sulphidation of fe rich host rocks with synchronous deposition of fe sulphides and gold however the variable nature of gold depositing reactions including lowering of fo 2 and ph allowed a multitude of small and some large deposits to form wherever that fluid circulation occurred in consequence several of the relatively small deposits currently worked from open pit are hosted by ultramafic and felsic rocks there are few constraints on the source of components au s k co 2 added to gold deposits but even giant deposits such as the golden mile kalgoorlie could have formed from a realistic greenstone source volume ca 8 8 5 km convective circulation of fluids could have contributed to the generation of high fluid rock ratios on the regional scale the markedly heterogeneous distribution of large gold deposits gold productivity and host rocks to deposits can be accommodated by the metamorphic replacement model the most favourable conditions for development of auriferous hydrothermal systems operated in younger ca 2 7 0 1 ga rift phase greenstones where greatest extension and crustal thinning produced high geothermal gradients crustal scale synbasinal faults and rapid extrusion and burial of volcanics including abundant komatiites iron rich tholeiitic basalts and dolerites were preferred host rocks for large gold deposits the least favourable conditions existed in older ca 3 5 3 4 ga platformphase greenstones where gentle sagging on submerged continental crust produced eruption of mainly mafic volcanics with few komatiites commonly in very shallow water environments this allowed intense synvolcanic alteration of both gold source rocks and potential host rocks the generally smaller gold deposits formed mainly in ultramafic or greywacke hosts younger ca 3 0 ga platform phase greenstones appear intermediate in nature but unlike other greenstones have significant epigenetic gold deposits in originally oxide facies bif which were deposited on relatively deep water platforms similar controls appear to exist on a world scale with gold mineralization peaking at ca 2 7 0 1 ga in response to development of major rift zones in thickened relatively mature continental crust interestingly the giant witwatersrand goldfield formed at about the same time

green s function approximation from cross correlations of 20 100 hz noise during a tropical storm approximation of green s functions through cross correlation of acoustic signals in the ocean a method referred to as ocean acoustic interferometry is potentially useful for estimating parameters in the ocean environment travel times of the main propagation paths between hydrophone pairs were estimated from interferometry of ocean noise data that were collected on three l shaped arrays off the new jersey coast while tropical storm ernesto passed nearby examination of the individual noise spectra and their mutual coherence reveals that the coherently propagating noise is dominated by signals of less than 100 hz several time and frequency noise normalization techniques were applied to the low frequency data in order to determine the effectiveness of each technique for ocean acoustic applications travel times corresponding to the envelope peaks of the noise cross correlation time derivatives of data were extracted from all three arrays and are shown to be in agreement with the expected direct surface reflected and surface bottom reflected interarray hydrophone travel times the extracted green s function depends on the propagating noise the green s function paths that propagate horizontally are extracted from long distance shipping noise and during the storm the more vertical paths are extracted from breaking waves

fluid infiltration into fault zones chemical isotopic and mechanical effects fluid infiltration into fault zones and their deeper level counterparts brittle ductile shear zones is examined in diverse tectonic environments in the 2 7 ga abitibi greenstone belt major tectonic discontinuities with lateral extents of hundreds of kilometres initiated as listric normal faults accommodating rift extension and acted as sites for komatiite extrusion and locally intense metasomatism during reverse motion on the structures accommodating shortening of the belt these transcrustal faults were utilised as a conduit for the ascent of trondhjemitic magmas from the base of the crust and of alkaline magmas from the asthenosphere and for the discharge of thousands of cubic kilometres of hydrothermal fluids such fluids were characterised by 18o 6 2 d 50 20 13c 4 4 and temperatures of 270 to 450 c probably derived from devolatilisation of crustal rocks undergoing prograde metamorphism hydrothermal fluids were more radiogenic 87sr 86sr 0 7010 to 0 7040 and possessed higher than did contemporaneous mantle komatiites or tholeiites and thus carried a contribution from older sialic basement a provinciality of87sr 86sr and 13c is evident signifying that fault plumbing sampled lower crust which was heterogeneous at the scale of tens of kilometres mineralised faults possess enrichments of large ion lithophile lil lil elements including k rb ba cs b and co2 and rare elements such as au ag as sb se te bi and w fluids were characterised by xco2 0 1 neutral to slightly acidic ph low salinity 3 wt k na 0 1 they carried minor ch4 co and n2 and they underwent transient effervescence of co2 during decompression clastic sediments occupy graben developed at fault flexures the40ar 39ar release spectra indicate that fault rocks experienced episodic disturbance on time scales of hundreds of millions of years

hydration of an active shear zone interactions between deformation metasomatism and magmatism the spinel lherzolites from the montferrier southern france oligocene basalts abstract geochemical and textural investigations have been simultaneously performed on spinel lherzolite xenoliths from the oligo miocene alkali basalts of montferrier southern france all the investigated samples have undergone a deformation very particular by intense shearing under high stresses up to 1 75 kbar low temperatures 900 c and strain rates of about 10 18 to 10 15 s 1 mineral chemistry reveals that the montferrier lherzolites are fragments of an undepleted relatively shallow upper mantle level located at a depth of 50 km 15 kbar moreover na and ti enrichment in diopside would reflect a metasomatic event also emphasized by the common occurrence of pargasite in 50 70 of the investigated samples crystallization of this amphibole is attributed to a hydrous infiltration which is related in time and space to the deformation indeed amphibole is preferentially concentrated in strongly deformed zones and in kink band boundaries of orthopyroxene porphyroclasts moreover the grain boundaries were used by the pervasive agent to percolate into the lherzolite significant chemical variations increase in mgo 15 and decrease in al 2 o 3 55 are observed within the range of 7 5 m adjacent to the grain boundary finally sr isotopic data 87 sr 86 sr demonstrate that the amphibole i e the metasomatic agent is genetically related to the host lava of the xenoliths thus the hydrous silicate liquid from which the amphibole has crystallized may be an early percolation of the ascending alkali magma this silicate liquid hydrated the shear zone located at a depth of 50 km induced the hydraulic fracturation of the lherzolite and the magmatic conduit opening subsequently the alkali magma sampled some fragments of this strongly deformed and metasomatized undepleted upper mantle level and brought them to the surface

geoacoustic inversion of ambient noise a simple method the vertical directionality of ambient noise is strongly influenced by seabed reflections therefore potentially geoacoustic parameters can be inferred by inversion of the noise in this approach using vertical array measurements the reflection loss is found directly by comparing the upward with the downward going noise theory suggests that this simple ratio is in fact the power reflection coefficient potentially a function of angle and frequency modeling and parameter searching are minimized and the method does not require a detailed knowledge of the noise source distribution the approach can handle stratified environments and is believed to tolerate range dependence experimental data from five sites four in the mediterranean one on the new jersey shelf are described most of the mediterranean sites had temporally varying noise directionality yet yielded the same reflection properties as one would hope one site was visited in conditions of very low surface noise this paper concentrates on an experimental demonstration of the feasibility of the method and data quality issues rather than automatic search techniques for geoacoustic parameters

filling up the shelf a sedimentary response to the last post glacial sea rise abstract following the last glacial maximum lgm lowstand global sea level rose by 120 m flooding previously exposed continental shelves worldwide with water and sediments in these drowned environments sediment accumulation patterns are dictated by a superposition of vertical tectonic motion sea level change and sediment supply rates which are hard to distinguish from one another this study focuses on a unique region where the first two components are known and well constrained the terminal part of the nile littoral cell along the eastern mediterranean continental margin data analysis is based on detailed interpretation of four newly obtained high resolution seismic reflection surveys integrated with two industrial seismic surveys the age of sedimentary sequences is constrained by correlation with drillholes while accumulation patterns strongly correlate with the local model based sea level curve our sub meter resolution seismic stratigraphy reveals post lgm shoreline migration and suggests a seismic based sea level curve since data presented here provide the first direct insight into the sedimentary accumulation pattern they are used to calibrate the modeled curve this simple yet innovative approach stresses the importance of high resolution seismic reflection data to sea level research worldwide while serving as a reference for the entire mediterranean sea

archean lamprophyre dykes and gold mineralization matheson ontario the conjunction of lile enriched mafic magmas deep crustal structures and au concentration at the canadian arrow deposit matheson separate base and precious metal bearing fracture arrays are associated with a trondhjemitic stock transected by lamprophyre dykes peripheral to the stock high fe tholeiitic pillow basalts fe2o3 17 8 wt tio2 2 4 wt al2o3 tio2 13 7 with interbedded felsic units experienced amphibolite facies hydrothermal or regional metamorphism and intense ductile deformation focussed within mylonite zones at the interflow horizons the trondhjemite stock experienced pervasive reaction with marine water at temperatures that diminished to 150 c this was accompanied by conversion of plagioclase of igneous origin to albite concomitant enrichment of sodium na2o 8 32 1 16 wt 1 and shifts of albite up to 18o 14 with attendent variably negative quartz albite fractionations galena dominated veins were precipitated at 220 255 c from hypersaline cacl2 nacl hydrothermal fluids with 22 34 equivalent wt nacl 18o 0 6 to 2 5 these were of evolved mar