contrasting arc and morb like assemblages in the paleoproterozoic flin flon belt manitoba and the role of intra arc extension in localizing volcanic hosted massive sulphide deposits the flin flon belt trans hudson orogen manitoba and saskatchewan is the largest paleoproterozoic volcanic hosted massive sulphide vms district in the world with 118 7 million tonnes mt of z

petrogenesis of intermediate volcanic assemblages from the shebandowan greenstone belt superior province evidence for subduction during the neoarchean abstract research on the petrogenesis of andesites and their implications for geodynamic setting are an important facet to understanding controversial tectonic processes during the archean the genesis of archean intermediate volcanic rocks and their relationship to mantle and crust derived melts can either support subduction dominated tectonic processes or plume crust interactions this study describes the lithogeochemistry and nd isotopic composition of intermediate volcanic assemblages in the shebandowan greenstone belt of the wawa abitibi terrane that were deposited prior to deformation and tectonic assembly of the superior province the intermediate rocks of the shebandowan greenstone belt are unique in that they are voluminous are relatively weakly deformed and are low metamorphic grade and contain significant amounts of magnesian andesites and adakites the major and trace element geochemistry of the intermediate assemblages share many of the geochemical characteristics of modern volcanic and continental arcs these features include enriched th nb and th la ratios steeply dipping rare earth patterns and pronounced negative ti and nb anomalies on primitive mantle normalized diagrams additionally these rocks also contain distinct positive pb and cs anomalies without evidence of major mobility of these elements during secondary processes neodymium isotopic analyses indicate the interaction with older crust and show good correlations with evolved nd isotopic values with other crustal contamination proxies such as th ce and ti sc ratios modeling mixing and assimilation fractional crystallization interactions between plume derived and crustal melts reveal that plume crust interactions cannot explain the compositional array obtained from the intermediate rocks in the shebandowan greenstone belt a compilation of u pb geochronology for the shebandowan greenstone belt reveals that tholeiitic komatiite dominated strata are slightly older than the intermediate dominated strata given that these domains are structurally separated it is very likely that the shebandowan greenstone belt was formed in two different geodynamic settings these different geodynamic settings have important implications for the metallogeny of the belt and explain the relative enrichment of au and ni cu mineralization in the shebandowan greenstone belt relative to other ca 2720 ma assemblages in the wawa abitibi terrane

field design and operation of a novel deepwater wide azimuth node seismic survey many new deepwater subsalt gulf of mexico developments are afflicted by poor imaging caused by the complex nature of their salt overburdens the atlantis field is an example a poor image of its northern flank hindered development the ocean bottom seismic obs autonomous node method was applied with the goal of substantially improving the subsalt reservoir image

from hot to cold the temperature dependence on rock deformation processes an introduction abstract understanding rock deformation processes in solid earth materials from the crystal to the tectonic plate scale is essential for characterising the evolution of the lithosphere and for predicting how rocks behave in the subsurface temperature is a key parameter that determines what rock deformation processes are active and therefore how tectonic structures form moreover it controls the migration of fluids and melt in the earth s crust that lead to phase transformations and changes in rock rheology this special issue gathers a collection of research papers following the 21st international conference on deformation mechanisms rheology and tectonics drt 2017 which was held in inverness scotland in april may 2017 organised by the university of aberdeen these contributions provide a significant advance in the study of rock deformation and fluid melt migration at multiple crustal levels from deformation bands near the earth s surface to shear zones in partially molten rocks in the lower crust in this introductory article we first provide an overview of how temperature controls deformation mechanisms and processes and then introduce the collection of research papers ordered from those analysing deformation processes occurring at high temperatures to contributions reporting deformation at shallow crustal conditions

reverse time migration a prospect of seismic imaging methodology abstract reverse time migration rtm is a seismic imaging method to map the subsurface reflectivity using recorded seismic waveforms the practice in exploration seismology has long established a two fold approach of seismic imaging using velocity modeling building to establish the long wavelength reference velocity models and using seismic migration to map the short wavelength reflectivity structures among various seismic migration methods for different situations rtm is the only method that is capable to use all seismic wave types that can be computed numerically being initiated in early 1980 s rtm seeks an image of the subsurface reflectivity as the best match in an image space between the extrapolation of time reversed waveform data and the prediction based on estimated velocity model and source parameters judging the image quality in the same space of forming the images is more advantageous than the approaches of modeling and inversion which seek the solution in the model space but judge its fitness in data space considering that most seismic migration applications today still use primary reflection as the only signal the capability of rtm to use all computable wave types is unique and helpful reducing the imaging artifacts due to mistaking non primary waves as primary reflections hence we refer to those rtm algorithms using only primary reflections as the first generation rtm methods and the rtm algorithms making a full use of primary reflections multiple reflections and other non primary waveform data as the second generation rtm methods this paper reviews the development history of the rtm along with its major challenges current solutions and future perspectives

the role of granitic intrusions in the evolution of the abitibi belt canada abstract the abitibi greenstone belt canada constitutes a segment of a broad volcanic arc that experienced three distinct periods of volcanic activity peaking at 2730 2725 2718 2714 and 2705 2700 ma during all three volcanic episodes which were generated by subduction related processes mantle plume derived komatiitic volcanic rocks were also added to the composite abitibi arc plume activity resulted in local regional extension and restricted later volcanism within the belt north south shortening produced thrusts and folds followed by se trending dextral strike slip faults between 2700 and 2692 ma the principal belt wide deformation subsequent e w dextral strike slip faulting limited to the major faults continued to 2690 2680 ma destor porcupine fault and even to 2680 2670 ma cadillac larder fault extensional structures resulting from the thickened crust developed around 2660 ma granitic intrusions are associated with all the volcanic episodes and phases of deformation and have been used to constrain the age of many of these events their role in stabilizing and adding to the volcanic crust is perhaps less well appreciated large synvolcanic tonalite dominated intrusions of the tonalite trondhjemite granodiorite ttg suite are associated with the three major periods of volcanic activity of the abitibi greenstone belt and are genetically related to the volcanism these synvolcanic intrusions occur both as high level flat cauldron subsidence complexes and as batholithic masses at the base of the oceanic crust tonalite gneiss dated from 2714 to 2703 ma occurring in structural culminations is considered to be arc underplated material the gneiss crystallized at depth and in contrast to the other tonalites does not appear to have intruded volcanic rocks the gneisses also record the earliest compressional deformation numerous intrusions of island arc affinity both the ttg and monzodiorite mzd suites form stocks and small plutons emplaced during the late phases of major deformation these are more numerous than voluminous and most of the tonalite end members of the suites probably intruded deeper within the sequence retarded by the now thickened crust large tonalite intrusions dominate the uplifted deeper sections adjacent to the abitibi belt in the kapuskasing uplift and grenville parautochthon and presumably make up much of the deep crust of the abitibi belt imaged in lithoprobe seismic profiles small stocks and dyke complexes characterize the late localized strike slip deformational phase these intrusions are porphyritic syenites and related rocks including some alkaline compositions garnetiferous granites of crustal derivation were emplaced in the final period of extensional activity around 2660 ma thus plutonic rocks are a volumetrically major overall component of the abitibi belt and were implicated in every phase of its development from early volcanic arc magmatic activity through the various stages of deformation to final stabilization as continental crust

upper mantle processes beneath the 2 7 ga abitibi belt canada a trace element perspective abstract mantle processes associated with volcanism in the abitibi belt remain poorly understood despite numerous detailed studies of its volcano sedimentary successions this paper employs log plots of nb y and zr y to distinguish the sources of well defined abitibi volcanic suites and to clarify processes in the upper mantle during greenstone belt development mafic rocks of the southern volcanic zone in the abitibi belt define two main trends on log plots of nb y versus zr y trends for the kidd munro assemblage and malartic block correspond to mixtures of strongly deleted plume asthenosphere and adakitic melts the shared trace element systematics of these volcanic successions confirm they are parts of a single authochthonous supracrustal assemblage that extended across the southern abitibi belt the younger kamiskotia assemblage and blake river group correspond to crustal extension episodes within an abitibi island arc trace element plots establish that they were derived from mantle plume related asthenosphere and not the late archean morb source upper mantle associated with island arc assemblages elsewhere in the southern superior province the data suggests widespread lateral flow of mantle plume asthenosphere occurred in the vicinity of the abitibi arc mantle mixing with adakitic melts continued between 2716 and 2698 ma the data are not consistent with wet komatiite models that generate ultramafic volcanic rocks from typical upper mantle following hydration of a mantle wedge chemical mixing trends for mafic magma sources indicate melt hybridization of the abitibi mantle wedge the trends require a slab melt origin for adakitic magmas rather than internal differentiation of underplated mafic crust comparisons with other 2 7 ga greenstone belts suggest that mantle plume interaction with archean subduction zones as proposed for the abitibi belt can be distinguished in the nb zr y systematics of associated mafic volcanic rocks

sm nd and sr isotope systematics of scheelite from the giant au w deposit muruntau uzbekistan implications for the age and sources of au mineralization the application of the sm nd isotope system of scheelite to dating of low sulfide quartz vein hosted au mineralization is still under discussion in the present work new sm nd and rb sr data for scheelite from the giant muruntau myutenbai au deposit kyzylkum western uzbekistan are discussed based on the geological relationship mineralogical properties and trace element characteristics two types of scheelite can be distinguished within the deposit the first one is represented by early bluish luminescent and weakly coloured scheelite generation 1 found within strongly deformed flat quartz veins the apparent isochron defined by this scheelite 351 22 ma is interpreted as a mixing line typically brownish to orange and yellowish luminescent scheelite from steeply dipping veins generation 2 defines a sm nd isochron age of 279 18 ma end 9 5 0 3 mswd 1 5 no evidence for mixing or disturbance by late alteration were found for these scheelites this sm nd isochron age agrees with the rb sr and k ar age range for wall rock alteration in this deposit reported previously the age of 280 ma is interpreted to date the high grade ore formation in the muruntau deposit there are currently no reliable age data available on the magmatic events in the muruntau region probably there is some overlap in time of the hercynian gold deposition with the intrusion of lamprophyric dykes the nd and sr isotopic signatures of scheelite define the wall rocks mainly metasiltstones and metasandstones as the most probable sources for these elements in scheelite

geochemistry of the dundonald komatiite basalt suite and genesis of dundeal ni deposit abitibi subprovince canada the genesis of konatiites basalts and associated ninineralization in the dundonald township area on tario is critical to understanding the metallogenic evolution of the kidd munro assemblage one of the most primitive volcanic assemblages in the world the 2 5 kin thick stratigraphic succession has a basal calc alkalic basalt dacite rhyolite sequence 2716 8 2 1 ma u pb zircon cut by the dundonald peridotite gabbro sill 27077 ma u pb zircon overlain by komatiitic and basaltic flows containing magmatic ni sulfide mineral ization which are in turn overlain by chemically distinctive low ti basalt flows the dundonald komatiites correlate with komatiites in the footwall of the giant kidd creek volcanic associated massive sulfide deposit 40 km to the west but are slightly older than the komatiites of munro township which are 40 km to the east the dundonald komatiites comprise a munro type al undepleted komatiite suite with liquid compositions having a120 ffio o 18 to 22 and mgo up to 30 3 vet percent anhydrous n 24 most samples in the ko matiite suite have slightly depleted light bee contents with lan smn 0 6 to 1 1 and lan ybn 0 4 to 0 9 n 21 and negligible ti ti and zr zr anomalies their major and trace element geochemistry is consistent with a derivation by sigfificant partial melting of a chemically primitive mantle with little or no influence of majoritc garnet flows that are host to the dundeal and alexo ni deposits have distinctively high thpm nbpm ratios 1 7 n 3 suggesting crustal contamination and peperite textures that are consistent with contami nation from nearby graphitic argillite the chemically distinctive lmv ti basalts have 49 to 53 percent sios 4 5 to 9 5 percent mgo 18 8 to 21 5 percent a1203 0 30 to 0 37 percent tios moderately depleted light ree con tents with lan smn 0 9 to 1 2 and la n ybn 0 4 to 0 6 high ni cr and ba contents 570 6 800 390 630 90 320 ppm respectively n 6 their high ai203 contents place them in the calc alkalic field on a jensen cation plot although their trace element ratios zr y la yb are more consistent with a tholeiitic affinity they are compositionally identical to and they correlate with low ti basalts in the kidd creek volcanic complex their geochemistry is consistent with a derivation by partial melting of a refractory harzburgitic mantle that has undergone a previous melt extraction possibly influenced by a large ion lithophile enriched hydrous phase the empire flow is the thickest and most primitive komatiite flow and is host to the dundeal ni deposit re source of 0 4 mt at 2 0 ni the empire flow contains an elongate dunite peridotite basal unit interpreted as the core of a flow that thermally eroded into footwall heterolithic breccias and pillowed andesites the main dundeal ni horizon overlies part of the basal dunite peridotite unit within the flow channel and extends over the cutbank wall the dundeal deposit and the nearby dundonald south ni deposit have lo v total sulfide con tents and high ni s ratios 0 9 and 1 0 respectively in comparison to most komatiite hosted magmatic sulfide deposits the high ni tenor in sulfide is believed to be due to assimilation of reducing carbonaceous sediment which causes greater ni partitioning into the magmatic sulfide phase

automated coregistration of repeat digital elevation models for surface elevation change measurement using geometric constraints a large archive of digital elevation model dem data spanning more than a decade is now available for a wide range of earth surface process studies precise coregistration is a critical step for obtaining accurate elevation change measurements from repeat dems we present an algorithm for coregistering stereoscopic gridded dems that includes an automatic detection of control surfaces a reliable estimation technique for defining a geometric relationship between dems through a 3 d conformal transformation and a quality check qc for the confidence of the coregistration for the control surface detection we use a geometric constraint approach that uses similarities in slope aspect and height undulation as observation weights in an iterative transformation model solution the qc is possible through the evaluation of the geometric similarities and the amount of detected relatively unchanged surfaces we test our algorithm using a sample of repeat stereoscopic gridded dems from multiple sources over a rapidly changing glacier in greenland the algorithm results on average in a 24 decrease in the standard error as obtained from elevation over stationary surfaces the result is not sensitive to the distribution of the control surface the qc metric provides a simple and effective criterion for parsing result quality in large data sets surface height decreases of 110 and 200 m at the up glacier and down glacier ends of kangerdlugssuaq glacier in greenland are observed between april 2001 and june 2010 respectively

benefits of full azimuth and ultralong offset data for subsalt imaging in the deepwater gulf of mexico abstract in deepwater regions of the gulf of mexico the ability to image subsalt structures has improved significantly with wide azimuth data reverse time migration and anisotropic tomography and imaging however subsalt imaging such as imaging steeply dipping salt flanks and subsalt three way closures still remains difficult in areas with complex salt geometry moreover limited subsalt illumination provides insufficient incident angles for residual curvature tomographic analysis full azimuth and long offset acquisition configurations are the latest acquisition technologies designed to address these subsalt challenges an improved subsalt imaging and tomography updating using staggered acquisition provides full azimuth data coverage and ultralong offsets

u pb ages and tectonic significance of late archean alkalic magmatism and nonmarine sedimentation timiskaming group southern abitibi belt ontario the paper presents u pb ages for zircons of the calc alkalic to alkalic igneous suite and associated alluvial fluvial sedimentary rocks of the timiskaming group in the late archean abitibi greensto

accuracy assessment of global barotropic ocean tide models the accuracy of state of the art global barotropic tide models is assessed using bottom pressure data coastal tide gauges satellite altimetry various geodetic data on antarctic ice shelves and independent tracked satellite orbit perturbations tide models under review include empirical purely hydrodynamic forward and assimilative dynamical i e constrained by observations ten dominant tidal constituents in the diurnal semidiurnal and quarter diurnal bands are considered since the last major model comparison project in 1997 models have improved markedly especially in shallow water regions and also in the deep ocean the root sum square differences between tide observations and the best models for eight major constituents are approximately 0 9 5 0 and 6 5 cm for pelagic shelf and coastal conditions respectively large intermodel discrepancies occur in high latitudes but testing in those regions is impeded by the paucity of high quality in situ tide records long wavelength components of models tested by analyzing satellite laser ranging measurements suggest that several models are comparably accurate for use in precise orbit determination but analyses of grace intersatellite ranging data show that all models are still imperfect on basin and subbasin scales especially near antarctica for the m2 constituent errors in purely hydrodynamic models are now almost comparable to the 1980 era schwiderski empirical solution indicating marked advancement in dynamical modeling assessing model accuracy using tidal currents remains problematic owing to uncertainties in in situ current meter estimates and the inability to isolate the barotropic mode velocity tests against both acoustic tomography and current meters do confirm that assimilative models perform better than purely hydrodynamic models

high resolution depth and coastline over major atolls of south china sea from satellite altimetry and imagery abstract current bathymetric models for the south china sea scs are largely based on predicted depths from gravity and sparse single beam echo sounder measurements such models lack high resolution coastlines and shallow water bottom features around atolls and islands this study refines the gravity field of the scs using sea surface heights from measurements of satellite altimeter geosat gm ers 1 gm jason 1 gm and the original cryosat 2 a new one minute gravity anomaly grid is determined the modeled gravity anomalies show a 6 mgal rms discrepancy with shipborne measurements in shallow waters an altimeter only bathymetric model is derived from the new gravity grid by the gravity geological method that uses the latest global and regional models of the ocean depth and marine gravity as a priori knowledge the new model outperforms current scs bathymetric models and is accurate to 100 m based on comparison with multi beam depth measurements optical images from ikonos 2 quickbird 2 geoeye 1 worldview 1 2 and 3 are rectified and digitized to derive the zero coastline and 20 m depth contours reef lines around 44 atolls which are integrated with the altimeter only depths giving significantly improved accuracies and spatial resolutions in modeled depths the improvement percentages of coastlines by the satellite imagery range from 50 to 97 at 41 of the 44 atolls we establish a webpage for free access to the optical and depth images and the depth and gravity grids we will continue to update satellite images altimeter derived gravity grids and bathymetric models over major atolls of the scs

archean neptunian fissures and early history of the destor porcupine fault zone timmins ontario canada neptunian dikes and fissures are intimately associated with a minor archean sedimentary basin near timmins ontario in the southwestern part of abitibi subprovince of the canadian shield these structures are associated with the late archean timiskaming unconformity and were formed by clastic sedimentation in fissures opened by the reactivation and dilation of basement faults along a major crustal shear a pull apart origin is indicated for the sedimentary basin by published township maps and the underground geology of the dome gold mine the neptunian dikes and fissures are discussed in relation to previous stratigraphic and tectonic interpretations of the timmins area

3d reconstruction of volcanic and ore forming environments of a giant vms system a case study from the kidd creek mine canada abstract the archean north rhyolite is a bimodal suite of rocks located directly northwest of but structurally separate from the kidd creek volcanogenic massive sulfide deposit which has produced 140 4 million tonnes of ore grading 2 29 wt cu 6 15 wt zn 0 22 pb and 86 2 g t ag the stratigraphy of the north rhyolite is identical to that of the kidd creek mine consisting from oldest to youngest of ultramafic flows aphyric rhyolite quartz porphyritic rhyolite and basalt flows divisible into a low tio2 basalt unit 1 55 wt with minor interflow graphitic argillites the north rhyolite is interpreted to be the folded continuation of the kidd creek mine stratigraphy similar alteration patterns in the north rhyolite and the kidd creek mine stratigraphy as well as significant copper and zinc values within the thickest portions of rhyolite domes and ridges of the north rhyolite suggests the potential for economically significant mineralization within the north rhyolite stratigraphy correlation between alteration mineralization and the rhyolite domes and ridges demonstrate the volcanic structures through which the rhyolite was extruded also acted as hydrothermal fluid pathways and were controlling structures in ore formation a 3d volcanic reconstruction showing the paleo seafloor at the time of ore formation illustrates that the rhyolite flows of the north rhyolite were emplaced into the same subsidence structure as the strata of the kidd creek mine area this 3d model generated by translating complex geological data acquired through core logging and underground mapping indicates the volcanic setting of and ore forming environment at kidd creek is much larger than previously thought and provides new spatial data that can be used in exploration targeting

internal structure of the cadillac tectonic zone southeast of val d or abitibi greenstone belt quebec the kirkland lake larder lake cadillac break is a major fault zone of the abitibi greenstone belt well known for its spatially associated gold camps a detailed structural analysis of this fault zone in the val d or area has shown the presence of a 200 750 m wide zone of high strain defined here as the cadillac tectonic zone ctz which includes the narrower schist zone generally regarded as the cadillac break the boundaries of the ctz which coincide with major lithologic contacts strike approximately east west and dip 80 to the north the internal structure of the ctz is best analysed in terms of two increments of the same progressive deformation the d1 strain increment is characterized by an east west striking subvertical s1 foliation at low angle in strike to the bound aries of the ctz and containing subvertical elongation lineation primary lithological contacts have been transposed into s1 and folded by f1a folds f1b intrafolial folds of s1 ranging from noncylindrical subhorizontal f

structural history of the manitouwadge greenstone belt and its volcanogenic cu zn massive sulphide deposits wawa subprovince south central superior province structural analysis of the manitouwadge greenstone belt integrated with detailed mapping and geochronological and petrographic studies reveals a complex early deformation history that significant

seismic evidence for preservation of the archean uchi granite greenstone belt by crustal scale extension abstract in the westernmost superior province of canada the east west alignment of granite greenstone belts and the adjacent highly deformed gneiss belts led to the first proposals that plate tectonics existed before 2 5 ga ago with the belts thrust against one another by east west oriented subduction zones here we present seismic reflection data which demonstrate that in this region the present juxtaposition of the uchi granite greenstone belt and the north caribou gneiss terrane occurred along a late southeast dipping extensional shear zone that extends from the surface into the lower crust the preservation of the uchi belt and probably the english river metasedimentary belt is directly related to their dropping along extensional shear zones which limited subsequent erosion the relative lateral transport of these greenstone rocks implies that they were neither derived from the immediately underlying crust nor preserved by vertical crustal movements as might occur in the absence of plate tectonics extension may have been associated with the emplacement of mantle derived magmas at 2700 ma which has been linked to slab break off or lithospheric delamination making the extension approximately coeval with local gold mineralisation since crustal scale faults can facilitate the circulation of gold bearing fluids we suggest that greenstone rocks preserved in the hanging walls of syn to post accretion extensional shear zones may preferentially host archean lode gold deposits in the westernmost superior province our seismic observations imply that some of the late structures in the well developed belts defined by surface mapping arose through the collapse of a collage of laterally accreted terranes

subaqueous calderas in the archean abitibi greenstone belt an overview and new ideas abstract the 300 700 km abitibi greenstone belt in canada contains numerous world class archean volcanogenic massive sulfide vms deposits yet documentation of archean subaqueous calderas hosting such deposits is lacking the modern sunrise deposit in the myojin knoll caldera of the izu bonin arc shows that submarine calderas are first order sites for vms the hunter mine and normetal calderas as well as the blake river megacaldera complex are reviewed with respect to geometry regional geology physical volcanology dyke emplacement and hydrothermal carbonate alteration these subaqueous calderas are placed into the geodynamic context of the abitibi greenstone belt the abitibi belt displays a complex history of oceanic arc formation evolution collision and fragmentation with numerous types of volcanic edifices and sedimentary basins controlled by oblique subduction and mantle plumes analogue models yielding new insights into the sequence of caldera forming events and their synvolcanic fault patterns are applied to explain archean examples underpressure experiments develop a consistent sequence of fault patterns that compare favourably with natural caldera events during subsidence two sets of faults propagate from the magma chamber margin 1 early reverse outward dipping faults and 2 normal inward dipping faults the largest massive sulfide deposits form preferentially at the caldera margin based on experimental studies and detailed facies mapping the hunter mine caldera is of the segmented piecemeal variety and the normetal caldera is akin to a piston structure the blake river megacaldera contains 1 the e w trending misema 2 the nw trending new senator and 3 the ne trending noranda calderas with the latter two being nested graben type calderas consistent with oblique archean subduction the poorly documented hydrothermal carbonate alteration is discussed and a new exploration model for calderas is presented the alteration study was evaluated at three levels microprobe analysis geochemical staining of drill core and whole rock analyses there were two principal stages of alteration related to vms formation an early silicification phase developed either at depth and or at the seawater interface whereby silicification was bedding parallel in fine grained volcaniclastic deposits near the water surface a pervasive and extensive semi conformable carbonate alteration zone with a discordant focused root zone along faults evolved subsequently three distinct carbonate pairings were observed 1 proximal siderite sideroplesite fe ankerite next to the vms deposit 2 an intermediate ankerite fe dolomite zone and 3 a distal calcite dolomite zone the carbonate phase is associated with the mineralizing event transitions between carbonate species are subtle and changes are indicated by mineral assemblage overlap the silica carbonate hydrothermal alteration pattern is a replacement product and is far more widespread than has been documented this alteration can be easily confused with primary carbonates and chemical precipitation deposits e g banded iron formation if detailed volcano sedimentary facies mapping with alteration has not been conducted and if outcrop is insufficient

gold mineralization at the syenite hosted beattie gold deposit duparquet neoarchean abitibi belt canada le gisement de beattie est situe dans la ceinture de roches vertes de l abitibi a proximite de la faille porcupine destor et est associe a une syenite porphyrique les corps mineralises ont une ressource totale inferee de 2 77moz contenu dans 56 2mt de minerai a 1 53g t d or dans le gisement de beattie deux styles de mineralisation sont presents a controle lithologique et a controle structural la mineralisation a controle lithologique est limitee exclusivement a la syenite alteree en carbonates de fer cette mineralisation represente du minerai a basse teneur mais fort tonnage dans lequel l or est porte par la pyrite arsenifere et l arsenopyrite l or est invisible il se presente sous la forme de solution solide dans le c ur poreux et riche en arsenic des pyrites la mineralisation a controle structural est presente uniquement dans des zones de cisaillement adjacentes et incluses dans la syenite le minerai est a haute teneur dans des zones de breches silicifiees a caractere hydraulique et tectonique dans des veines de quartz cherteux dans des veines polymetalliques intensement silicifiees et dans des dykes de syenite trachytique tres alteree l or y est visible sous forme d electrum dans les microfractures des pyrites brechifiees les deux styles de mineralisation et les alterations font partie d une evolution paragenetique commune dans un environnement magmatique hydrothermal des phases initiales oxydantes ont evolue en conditions reduites a la faveur de fluides magmatiques et externes riches en co2 ce changement d etat d oxydation a entraine la precipitation des sulfures et la cristallisation de l or invisible dans la pyrite arsenifere et l arsenopyrite une phase d alteration ulterieure dominee par des fluides hydrothermaux riches en silice a pour resultat la brechification des sulfures et leur redistribution dans des corridors siliceux ainsi que la remobilisation de l or dans les microfractures des pyrites brechifiees les compositions calculees de 18o et d sur les veines de quartz associees a cet evenement tardif sont respectivement 7 67 o et 66 o indiquant une dominance des fluides magmatiques avec une probable composante metamorphique cet evenement syn metamorphique transition d2 d3 est associe a un fort enrichissement en hg te mo ag sb as et se le style de cristallisation de l or dans le gisement de beattie est une consequence de la dominance des regimes en systemes ouverts tant au niveau de l incorporation dans le magma de l arsenic qui controle la precipitation de l or invisible que de la circulation tardive de fluides hydrothermaux riches en silice qui sont a l origine de la remobilisation de l or le gisement de beattie partage des affinites avec des gisements associes aux intrusions intrusion related gold deposit des gisements epithermaux a tendance neutre a intermediaire et des gisements de type mesothermaux mots cles de l auteur gisement d or porphyre archeen or invisible remobilisation de l or

development of sedimentary basins in the archean abitibi belt canada an overview sedimentation in the archean abitibi greenstone belt occurred during four depositional episodes i sedimentary cycle 1 2730 2720 ma ii sedimentary cycle 2 2715 2705 ma iii sedimentary cycle 3 2700 2687 ma and iv sedimentary cycle 4 2685 2675 ma records of the first two sedimentary cycles are preserved in basins within the northern volcanic zone whereas basins formed during the latter two sedimentary cycles are located within the southern volcanic zone of the abitibi belt sedimentary cycles 1 and 3 represent deep water facies as indicated by turbidites resedimented conglomerates pelagic sediments and ubiquitous iron formations subaerial deposits have not been identified in contrast sedimentary cycles 2 and 4 show a prevalence of fluvial to shallow water marine and or lacustrine deposits tectono magmatic influence on sedimentation during cycles 2 and 4 is documented by i the presence of numerous unconformities underlain by plutonic and volcanic rocks ii locally voluminous sh

u pb geochronology of the eastern abitibi subprovince part 2 noranda kirkland lake area u pb zircon ages for 15 volcanic and plutonic units in the noranda and kirkland lake areas help constrain the history of volcanism plutonism sedimentation and deformation in the south central part of the abitibi belt volcanism occurred over an interval of at least 50 ma beginning with the deposition of the volcanic and volcaniclastic units within the pacaud structural complex at 2747 ma following a period of apparent quiescence magmatism resumed at 2730 2725 ma with the eruption of volcanic rocks in the normetal and lac abitibi area from 2715 until about 2698 ma volcanism occurred sporadically throughout much of the area culminating in the eruption of the blake river group from 2703 to 2698 ma several large intrusive bodies yield ages that indicate that they are plutonic equivalents of the blake river group plutons that are considered to have been emplaced during the kenoran orogeny give ages that are only slightly younger than the youngest volcanic units of the blake river group emphasizing

timing and kinematics of post timiskaming deformation within the larder lake cadillac deformation zone southwest abitibi greenstone belt ontario canada the larder lake cadillac deformation zone is one of several anastomosing zones of high strain within the abitibi greenstone belt in the kirkland lake area ontario the larder lake cadillac de

enhanced prestack depth imaging of wide azimuth data from the gulf of mexico a case history we present a case study of enhanced imaging of wide azimuth data from the gulf of mexico utilizing recent technologies and we discuss the resulting improvements in image quality especially in subsalt areas relative to previous results the input seismic data sets are taken from many large scale wide azimuth surveys and conventional narrow azimuth surveys located in the mississippi canyon and atwater valley areas in the course of developing the enhanced wide azimuth processing flow the following three key steps are found to have the most impact on improving subsalt imaging 1 3d true azimuth surface related multiple elimination srme to remove multiple energy in particular complex multiples beneath salt 2 reverse time migration rtm based delayed imaging time dit scans to update the complex subsalt velocity model and 3 tilted transverse isotropic tti rtm to improve image quality our research focuses on the depth imaging aspects of the project with particular emphasis on the applicati

stratigraphic setting and timing of the montagne d or deposit a unique rhyacian au rich vms deposit of the guiana shield french guiana abstract in french guiana the montagne d or gold deposit 5 moz at 1 5 g t au is located in the northern branch of the rhyacian paramaca greenstone belt the sulphide deposit is hosted by a south facing bimodal volcanic and volcaniclastic sequence that is highly strained and affected by a penetrative e w striking and steeply south dipping foliation the volcanic sequence is composed of three members 1 the lower unit in the stratigraphic footwall 2 a bimodal mafic felsic formation hosting the orebody and 3 the upper sedimentary and volcanic rocks unit in the stratigraphic hanging wall the bimodal formation is dominated by calc alkaline felsic volcanic rocks in the west interbedded interdigitated with tholeiitic mafic rocks in the east pillowed mafic flows and graded bedded felsic volcaniclastic rocks collectively indicate effusive to explosive volcanic activity in a submarine environment the mineralization consists of thick and laterally extensive sulphide zones forming 1 stratiform sulphide disseminations 2 structurally transposed stringer stockworks and 3 thin layers of deformed semi massive sulphides the gold rich sulphide mineralization consists mainly of pyrite pyrrhotite and chalcopyrite with minor sphalerite magnetite galena and arsenopyrite hosted by chlorite sericite rich alteration zones mainly developed in the felsic tuff facies u pb zircon geochronology shows that most of the montagne d or volcanic and intrusive sequence has crystallized during a multi cycle magmatic event from ca 2152 ma to ca 2130 ma a porphyry intrusion crosscutting the ore yields a u pb zircon age of 2117 6 5 1 ma hence constraining a minimum age for the auriferous sulphide mineralization this also indicates that the sulphide mineralization was coeval with arc magmatism demonstrating the volcanogenic nature of the montagne d or gold deposit

structural setting of the young davidson syenite hosted gold deposit in the western cadillac larder lake deformation zone abitibi greenstone belt superior province ontario abstract within the southern abitibi greenstone belt of the superior province intrusion related in particular syenite hosted gold deposits represent a significant type that is poorly understood whether the gold mineralization is genetically linked to the syenite intrusions as in a magmatic model or structurally associated with the development of subsequent shear zones remains very controversial our new structural data show that the multiply deformed young davidson gold deposit and its surrounding matachewan area occur along the western extension of the cadillac larder lake deformation zone clldz a tectonically and economically important crustal scale deformation zone in the southern abitibi greenstone belt four generations d1 d4 of deformation are recognized the first part of the d1 deformation d1a records a ne sw oriented shortening and resulted in regional upright folding without penetrative foliation whereas the subsequent d1b generates regional penetrative foliations and top to ne reverse faults d2 occurs during a nw se oriented shortening and produces asymmetric folds oblique slip thrusts and dextral strike slip shear zones d3 semi brittle deformation refolds the d1 and d2 fabrics whereas the latest d4 sinistral fault records a paleoproterozoic brittle deformation the young davidson deposit is a lode gold deposit that at least in part was structurally controlled it is associated with the development of the clldz and hosted in a syenite four main generations of veins are identified in the syenite v1 veins are characterized by folded and boudinaged quartz ankerite veins v2 veins are represented by folded or en echelon quartz pyrite veinlets v3 veins are comprised of en echelon quartz carbonate veins with sulfide minerals and v4 veins consist of planar carbonate quartz veins and minor hematite petrological studies reveal that the major phase of gold mineralization is associated with the v2 veins and partially with the v3 veins gold mineralization and emplacement of the associated veins appear to have occurred during regional d1b ne sw oriented shortening and top to ne shearing and the syenite acted as a mechanical trap due to competency contrast to the wall rock

geology of the orogenic cheminis gold deposit along the larder lake cadillac deformation zone ontario the larder lake cadillac deformation zone llcdz is one of two major auriferous deformation zones in the southern abitibi subprovince of the archean superior province it hosts the cheminis and the giant kerr addison chesterville deposits within a strongly deformed band of fe rich tholeiitic basalt and komatiite of the larder lake group ca 2705 ma the latter is bounded on both sides by younger less deformed timiskaming turbidites 2674 2670 ma the earliest deformation features are f1 folds affecting the timiskaming rocks which formed either during d1 extensional faulting or during early d2 north south shortening related to the opening and closure respectively of the timiskaming basin continued shortening during d2 imbricated the older volcanic rocks and turbidites and produced regional f2 folds with an axial planar s2 cleavage d2 deformation was partitioned into the weaker band of volcanic rocks producing the strong s2 foliation l2 stretching lineation and south side up shear sense indicators which characterize the llcdz gold is present in quartz carbonate veins in deformed fuchsitic komatiites carbonate ore and turbiditic sandstone sandstone hosted ore and in association with disseminated pyrite in altered fe rich tholeiitic basalts flow ore all host rocks underwent strong mass gains in co2 s k2o ba as and w during sericitization carbonatization and sulphidation of the host rocks suggesting that they interacted with the same hydrothermal fluids textural relationships between alteration minerals and s2 cleavage indicate that mineralization is syn cleavage thus gold was deposited as hydrothermal fluids migrated upward along the llcdz during contractional d2 south side up shearing the gold zones were subsequently modified during d3 reactivation of the llcdz as a dextral transcurrent fault zone

coastline extraction from repeat high resolution satellite imagery abstract this paper presents a new coastline extraction method that improves water classification accuracy by benefitting from an ever increasing volume of repeated measurements from commercial satellite missions the widely used normalized difference water index ndwi method is tested on a sample of around 12 600 satellite images for statistical analysis the core of the new water classification method is the use of a water probability algorithm based on the stacking of repeat measurements which can mitigate the effects of translational offsets of images and the classification errors caused by clouds and cloud shadows by integrating quickbird worldview 2 and worldview 3 multispectral images the final data product provides a 2 m resolution coastline as well as a 2 m water probability map and a repeat count measurement map improvements on the existing coastline gshhs the global self consistent hierarchical high resolution shoreline database 50 m 5000 m in terms of resolution 2 m is substantial thanks to the combination of multiple data sources

stress arching and its impact on 4d seismic amplitudes and traveltimes abstract pressure depletion during production from a reservoir can cause geomechanical changes in both the reservoir and overburden dropping the pore pressure in the reservoir increases the load on the rock matrix resulting in compaction in most cases the magnitude of this compaction is negligible however when depletion pressures are large or when the reservoir rock is highly compressible the compaction may be significant as the reservoir pulls away from the surface of the earth a stress arch forms in the overburden with the vertical stress decreasing directly above the reservoir and increasing in the pillars of the stress arch these stress changes can perturb the seismic velocities which combined with the changes in path length to the reservoir can cause traveltime changes in the overburden the unloading of the overburden directly above the reservoir shields the reservoir from seeing the full change in pore fluid pressures and thus can have a significant impact on the amplitude changes in

geobarometry differential block movements and crustal structure of the southwestern abitibi greenstone belt canada the southern volcanic zone of the archean abitibi greenstone belt comprises several fault bounded tectonic blocks with distinct volcanic sedimentary sequences pressure temperature time p t t histories granite compositions and metallogenic provinces pressure distributions have been mapped out from an extensive new database derived from al in hornblende and other geobarometers in the composite crustal structure of the southern volcanic zone determined from the pressure time data the lacorne block and pontiac subprovince represent deeper crustal levels overlain by rocks exposed at the surface in the round lake or lac abitibi type blocks which are in turn capped by those exposed at the surface in a blake river rouyn type block exposure of the deeper crustal levels and juxtaposition of these distinct tectonic blocks are interpreted to have occurred by differential block uplift caused by strike slip faulting which was related to oblique collisional tectonics during late tectonic development of the superior province in late archean time

finely sampled 3d angle gathers from sparse obn data large scale deepwater ocean bottom node obn surveys typically use a node spacing of about 400 m we make 3d angle gathers from obn data by mapping image traces to the reflection azimuth and reflection angle domain large node spacing may coarsely sample the seismic data in these angles this may result in degraded and noisy angle gathers unless we properly account for the sampling during processing we describe a method for making high quality 3d angle gathers on finely sampled angle grids we do this by properly band limiting the mapping operator with sinc functions defined in the angle domain this method allows us to oversample the 3d angle gathers accurately in the angle domain and obtain high quality results we demonstrate our method with deepwater gulf of mexico node data and show that we can produce high quality gathers even with 800 m node spacing the angle gathers derived from these wider node data preserve residual moveout and therefore are suitable for model building our results add confidence that data acquired with nodes spaced farther apart than 400 m can be processed and imaged successfully

gold bearing fault zones related to late archean orogenic folding of upper and middle crust in the abitibi granite greenstone belt ontario abstract this work investigates the structures of the abitibi granite greenstone belt ontario with a focus on regional scale folds and on regional scale auriferous fault zones the folds and the fault zones resulted from late archean orogenesis the analysis is based on studies of surface geology and on modelling of the gravity field amphibolite grade orthogneiss was involved in the regional folding that also deformed the overlying greenstones folding resulted in uplift of the orthogneiss that preserves the metamorphic mineral assemblage ferropargasite garnet biotite andesine quartz geothermobarometric calculations indicate recrystallization of a metatonalite sample under peak paleopressures of 7 0 1 2 to 7 9 1 1 kb providing evidence that folding involved crust to depths of at least 18 25 km the regional bouger anomaly map reveals previously unrecognized first order folds interpretation of the bouger anomaly map also confirms that granitic batholiths are hosted by anticlines a wavelet based inversion method was used to determine the locations orientations and continuations at depth of the maxima of density contrasts the maximum density contrasts correspond to steeply dipping geological contacts on the limbs of the open to tight regional scale folds regional scale fault zones only have prominent gravity signatures where they correspond to sheared rocks on the limbs of folds modelled gravity profiles were used to produce profiles that visualize the shapes of batholiths and greenstone bodies within the present day upper crust the granitic batholiths have tabular shapes which are locally folded with preserved main body thicknesses of 1 3 km the greenstones form keels corresponding to synclines some of which reach 5 6 km depth the results of this study confirm that the principal deformational response of the abitibi granite greenstone belt to late archean collisional tectonics was large half wavelength 10 40 km folding of the upper and middle crust our results and interpretations also strongly suggest the regional scale fault zones which are loci for orogenic gold deposits are fold related structures they represent quasi continuous lineaments of shearing and faulting on the limbs of regional folds and locally in the cores of detachment anticlines as shown in a previous paper

4d history of the nimbus vhms ore deposit in the yilgarn craton western australia abstract due to its unique mineralogy in the archaean yilgarn craton the origin of the high grade nimbus ag zn au deposit has been contentious for a number of years recent interpretations of the deposit as a shallow water and low temperature volcanic hosted massive sulphide vhms deposit with epithermal characteristics i e a hybrid bimodal felsic deposit were based on detailed studies of its volcanology mineralogy hydrothermal alteration assemblages geochemistry multiple s isotopes and trace element content of sulphide however this model has been questioned in favour of a late epithermal fault hosted system effective greenfields exploration for similar deposits elsewhere requires a robust deposit model and well understood timing of ore formation we present a comprehensive multi disciplinary study to further constrain the processes involved in the evolution of nimbus and generate a 4d evolutionary model of the system host rock dacite formation is well constrained by shrimp u pb zircon geochronology to c 2703 ma re os ages for the first sulphide phase gives an imprecise maximum age to the ore formation of 2682 110 ma high precision pb isotope variations in ore stage and late galenas track changes in the sulphides over time complemented by new geochronology the pb isotope data indicates that the polymetallic ore precipitation happened at the same time as the volcanism with the second generation indicating minor local remobilisation of pb in late quartz carbonate veins at c 2630 ma 40ar 39ar dating of sericite altered plagioclase from foliated dacite and u pb shrimp dating of syn to post deformation monazites have yielded ages of 2630 ma the late event at c 2630 ma is most likely related to widespread late low ca granite emplacement across the eastern goldfields this study provides arguments that suggest that nimbus is a syn volcanic deposit the ore timing is consistent with the model of replacement type vhms deposit with the age of the main mineralisation similar to the age of the dacitic host rocks at 2703 ma the late event modifies the pre existing ore and overprints the previous ore related alteration ages from the altered plagioclase high precision double spiked pb isotope constraints from late quartz carbonate veins provides an opportunity to vector to hidden deposits

the setting style and role of magmatism in the formation of volcanogenic massive sulfide deposits throughout earth s history all volcanogenic massive sulfide vms hosting environments are associated with specific assemblages of mafic and felsic rocks with distinct petrochemistry petrochemical assemblages indicative of formation at anomalously high temperatures within extensional geodynamic environments in mafic dominated juvenile ophiolitic vms environments there is a preferential association with mafic rocks with boninite and low ti tholeiite mid ocean ridge basalt morb and or back arc basin basalt affinities representing forearc rifting or back arc initiation mid ocean ridges or back arc basin spreading or back arc basins respectively felsic rocks in juvenile oceanic arc environments in archean terrains are high field strength element hfse and rare earth element ree enriched in post archean juvenile oceanic arc terrains felsic rocks are commonly hfse and ree depleted and have boninite like to tholeiitic signatures in vms environments that are associated with continental crust i e continental arc and back arc and dominated by felsic volcanic and or sedimentary rocks evolved environments felsic rocks are the dominant hosts to mineralization and are generally hfse and ree enriched with calc alkalic a type and or peralkalic affinities representing continental arc rifts continental back arcs and continental back arcs to continental rifts respectively coeval mafic rocks in evolved environments have alkalic within plate ocean island basalt like and morb signatures that represent arc to back arc rift versus back arc spreading respectively the high temperature magmatic activity in vms environments is directly related to the upwelling of mafic magma beneath rifts in extensional geodynamic environments e g mid ocean ridges back arc basins and intra arc rifts underplated basaltic magma provides the heat required to drive hydrothermal circulation extensional geodynamic activity also provides accommodation space at the base of the lithosphere that allows for the underplated basalt to drive hydrothermal circulation and induce crustal melting the latter leading to the formation of vms associated rhyolites in felsic dominated and bimodal vms environments rifts also provide extensional faults and the permeability and porosity required for recharge and discharge of vms related hydrothermal fluids rifts are also critical in creating environments conducive to preservation of vms mineralization either through shielding massive sulfides from seafloor weathering and mass wasting or by creating environments conducive to the precipitation of subseafloor replacement style mineralization in sedimented rifts subvolcanic intrusions are also products of the elevated heat flow regime common to vms forming environments shallow level intrusive complexes i e within 1 3 km of the seafloor may not be the main drivers of vms related hydrothermal circulation but are likely the manifestation of deeper seated mantle derived heat i e 3 10 km depth that drives hydrothermal circulation these shallower intrusive complexes are commonly long lived i e millions of years and reflect a sustained thermally anomalous geodynamic environment such a thermally anomalous environment has the potential to drive significant hydrothermal circulation and therefore multi phase long lived subvolcanic intrusive complexes are excellent indicators of a potentially fertile vms environment the absence of intrusive complexes however does not indicate an area of low potential as they may have been moved or removed due to post vms tectonic activity in some cases shallow level intrusive systems contribute metals to the vms hydrothermal system

oblique archean subduction accretion and exhumation of an oceanic arc during dextral transpression southern volcanic zone abitibi subprovince canada abstract the archean abitibi subprovince divided into northern nvz and southern svz volcanic zones is characterized by the crustal scale destor porcupine manneville fault zone dpmfz which links the svz and nvz and the cadillac larder lake fault zone cllfz which separates the abitibi and pontiac subprovinces the dpmfz and cllfz represent major deformation zones that record over 60 million years of archean deformation the dextral transpressional phase in the nvz which represents incipient svz deformation occurred between 2700 and 2692 ma and is characterized by southeast se trending dextral faults e g macamic fault synorogenic flysch sedimentation is focussed at the interface between the svz nvz and pontiac abitibi subprovinces the se trending parfouru fault linking the two major trench fault systems is interpreted as a reactivated leaky transform fault and is associated with synorogenic flysch sedimentation the early monzodioritic suite of the preissac lacorne batholith was related to dpmfz thrusting ca 2692 2690 ma the change from early thrusting to transcurrent motion is recorded in the duparquet strike slip basin which formed between 2690 and 2680 ma along the dpmfz and the granada pull apart basin which evolved between 2680 and 2670 ma along the cllfz the timing of these basins indicates a diachronous evolution renewed thrusting affected the granada basin but not the northern duparquet strike slip basin so that a southward migrating deformation front is inferred late exhumation resulted in extension along both fault zones and was responsible for the juxtaposition of medium and low grade metamorphic rocks the monzogranitic suite of the lamotte pluton which occurred between 2660 and 2642 ma is linked to exhumation final dextral transpression post dating exhumation produced shearing and folding the svz of the abitibi subprovince shows the salient attributes of modern oblique orogenic collisions with alternating phases of thrusting and strike slip movement along crustal scale faults during dextral transpression

a coastline detection method in polarimetric sar images mixing the region based and edge based active contour models this paper proposes a coastline detection method for polarimetric synthetic aperture radar sar images based on region based and edge based active contour models it can be used to detect coastline accurately and fast in this method the region based and edge based active contour models are effectively combined by an important property of the likelihood ratio edge detector in polarimetric sar images which is proved by theory using low resolution image obtained by multilook processing we detect accurate and continued coarse coastlines by a region based level set method the property of the likelihood ratio edge detector of polarimetric sar images along the coastline region is then analyzed the coarse detection result is finally refined using a fast snake active contour model based on the edge property polarimetric sar data acquired by radarsat 2 over a singapore region and terrasar x over a berkeley region are both used to test the proposed algorithm the experimental results show that the coastline is fast and accurately detected in different initial scales the proposed method greatly reduces the data processing time compared with the coastline detection method based on a single scale

metamorphism in archaean greenstone belts calculated fluid compositions and implications for gold mineralization an inescapable consequence of the metamorphism of greenstone belt sequences is the release of a large volume of metamorphic fluid of low salinity with chemical characteristics controlled by the mineral assemblages involved in the devolatilization reactions for mafic and ultramafic sequences the composition of fluids released at upper greenschist to lower amphibolite facies conditions for the necessary relatively hot geotherm corresponds to those inferred for greenstone gold deposits xco2 0 2 0 3 this result follows from the calculation of mineral equilibria in the model system cao mgo feo al2o3 sio2 h2o co2 using a new expanded internally consistent dataset greenstone metamorphism cannot have involved much crustal over thickening because very shallow levels of greenstone belts are preserved such orogeny can be accounted for if compressive deformation of the crust is accompanied by thinning of the mantle lithosphere in this case the observed metamorphism which was contemporaneous with deformation is of the low p high t type for this type of metamorphism the metamorphic peak should have occurred earlier at deeper levels in the crust i e the piezothermal array should be of the deeper earlier type however at shallow crustal levels the piezothermal array is likely to have been of deeper later type as a consequence of erosion thus while the lower crust reached maximum temperatures and partially melted to produce the observed granites mid crustal levels were releasing fluids prograde into shallow crustal levels that were already retrograde we propose that these fluids are responsible for the gold mineralization thus the contemporaneity of igneous activity and gold mineralization is a natural consequence of the thermal evolution and does not mean that the mineralization has to be a consequence of igneous processes upward migration of metamorphic fluid via appropriate structurally controlled pathways will bring the fluid into contact with mineral assemblages that have equilibrated with a fluid with significantly lower xco2 these assemblages are therefore grossly out of equilibrium with the fluid in the case of infiltrated metabasic rocks intense carbonation and sulphidation is predicted if as seems reasonable gold is mobilized by the fluid generated by devolatilization then the combination of processes proposed most of which are an inevitable consequence of the metamorphism leads to the formation of greenstone gold deposits predominantly from metamorphic fluids

u pb geochronology of archean metasedimentary rocks in the pontiac and abitibi subprovinces quebec constraints on timing provenance and regional tectonics abstract u pb isotopic ages of single detrital zircons have been obtained from metasandstones in the northern part of the pontiac subprovince and from the cadillac kewagama and lac caste groups within the southern abitibi subprovince youngest detrital zircon ages from these sequences are 2685 2686 2687 and 2693 ma respectively the lac fourniere pluton which intrudes pontiac group metasedimentary rocks is dated at 2682 1 ma a similar age was previously measured from a pluton that cuts the kewagama group these data bracket deposition of greywacke in the pontiac and abitibi subprovinces to 2685 3 ma in contrast the youngest zircon found in a volcaniclastic unit interbedded with timiskaming group metawacke is 2673 2 ma while the age of a pluton that intrudes the timiskaming is 2672 1 ma thus the timiskaming group is distinctly younger than the other metasedimentary rocks the normalized probability distributions of detrital zircon ages from the pontiac and the abitibi metasedimentary rocks as well as of dated igneous rocks from the southern abitibi subprovince all show that their major zircon populations formed in the age range 2685 2710 ma the distributions for the abitibi metaturbidites and dated igneous rocks are very similar suggesting that metasedimentary rocks in the abitibi belt were mostly derived from the surrounding granite greenstone terrain the largest peak of the pontiac distribution is a few million years younger than that from the abitibi metasedimentary rocks but there is a correlation between major peaks and both groups show similar age ranges for older pre abitibi components 2750 2850 and 3020 3030 ma deposition of the ca 2685 ma sediments was virtually syn deformational based on previous field geochemical and isotopic studies as well as the detrital zircon age data the pontiac group may represent a foreland basin that may have developed from an accretionary prism the source of much of the sediment may have been an uplifted extinct continental arc to the north the arc was mostly eroded into the sediment basin and perhaps tectonically overridden by a southward advancing nappe complex comprised of its back arc basin now partly preserved in the southern volcanic zone of the abitibi subprovince metaturbidites exposed between metavolcanic assemblages within the greenstone belt may represent overturned unconformities at the structural base of the greenstones these were brought up by high angle faults which also localized deposition of non marine timiskaming type sediments it is tentatively suggested that pontiac type metasedimentary rocks extend most of the way beneath the abitibi subprovince the oldest part of the basin emerging as the quetico group in the western superior province

petrogenetic and geodynamic origin of the neoarchean dore lake complex abitibi subprovince superior province canada the neoarchean ca 2728 ma anorthosite bearing dore lake complex in the northeastern abitibi subprovince quebec was emplaced into an association of intra oceanic tholeiitic basalts and gabbros known as the obatogamau formation the obatogamau formation constitutes the lower part of the roy group which is composed of two cycles of tholeiitic to calc alkaline volcanic and volcaniclastic rocks siliciclastic and chemical sedimentary rocks and layered mafic to ultramafic sills in this study we report major and trace element results and nd sr pb and o isotope data for anorthosites leucogabbros gabbros and mafic dykes from the dore lake complex and spatially associated basalts and gabbros of the obatogamau formation to assess their petrogenetic origin and geodynamic setting field and petrographic observations indicate that the dore lake complex and associated volcanic rocks underwent extensive metamorphic alteration under greenschist facies conditions resulting in widespread epidotization 20 40 and chloritization 10 40 of many rock types plagioclase recrystallized mainly to anorthite and albite endmembers erasing intermediate compositions metamorphic alteration also led to the mobilization of many elements e g lile and transition metals and to significant disturbance of the rb sr and u pb isotope systems resulting in 1935 150 and 3326 270 ma errorchron ages respectively the sm nd isotope system was less disturbed yielding an errorchron age of 2624 160 ma on many binary major and trace element diagrams the least altered anorthosites and leucogabbros and the gabbros and mafic dykes of the dore lake complex plot in separate fields signifying the presence of two distinct magma types in the complex the gabbros and mafic dykes in the dore lake complex share the geochemical characteristics of tholeiitic basalts and gabbros in the obatogamau formation suggesting a possible genetic link between the two rock associations initial end 2 6 to 5 0 and 18o 6 1 to 7 9 values for the dore lake complex and gabbros of the obatogamau formation end 2 8 to 4 0 18o 7 3 to 8 0 are consistent with depleted mantle sources all rock types in the dore lake complex and the roy group share the trace element characteristics of modern arc magmas suggesting a suprasubduction zone setting for these two lithological associations on the basis of regional geology and geochemical data we suggest that the dore lake complex and the obatogamau formation represent a dismembered fragment of a suture zone like many phanerozoic ophiolites resulting from closure of a back arc basin between 2703 and 2690 ma

the macassa mine archean lode gold deposit kirkland lake ontario geology patterns of alteration and hydrothermal regimes the only remaining gold producer of seven interconnected mines the district has produced over 710 000 kg au since 1913 the area is underlain by part of the timiskaming group three types of gold ore 1 native au in chloritic fault gouge or small quartz lenses within a thrust fault system called break ore 2 gold bearing quartz veins in both hanging and footwalls of this fault system termed vein ore 3 several relatively wide zones of intensely fractured bleached silicified and pyritized rock containing lenses and pods of quartz with native au and telluride minerals called breccia ore the delta 18 o and delta d of rocks and mineral separates in these three ore types suggest that the ore was precipitated from hydrothermal fluids of delta 18 o 7 to 9 6 per mil and delta d 35 to 85 per mil at 350 degrees to 460 degrees c initial hydrothermal regime was followed by downward penetration of oxidizing sulfate bearing fluids delta 18 o 0 to 2 per mil delta d 20 to 70 per mil and of probable marine and or meteoric water origin initially at temperatures of 200 degrees c waning to 50 degrees c or less a third fluid regime is indicated for quartz magnetite chlorite veins which have mineral pair fractionations corresponding to fluids of delta 18 o 4 0 to 0 5 per mil and 210 degrees to 260 degrees c these three hydrothermal fluid regimes are interpreted to reflect a sequence of crustal compression relaxation and finally uplift above sea level probably all during the archean incremental 39 ar 40 ar upper plateau age of 2 575 m y for vein actinolite the deposit is interpreted to have formed during a period of major fracturing ductile deformation and thermal perturbation accompanying the episode of batholith emplacement modified journal abstract

constraints on the geodynamic evolution of the southern superior province u pb la icp ms analysis of detrital zircon in successor basins of the archean abitibi and pontiac subprovinces of ontario and quebec canada abstract to investigate the tectonic development of the southern superior province new u pb laser ablation inductively coupled mass spectrometry analysis of detrital zircon was conducted on graywacke samples from successor basins of the abitibi and pontiac subprovinces the three successor basin successions investigated are the 2690 2685 ma porcupine assemblage and the 2679 2669 ma timiskaming assemblage of the abitibi subprovince and the 2682 ma sedimentary rocks of the pontiac subprovince predominately neoarchean zircon grains 80 95 of the total zircon population reflect local sources in the abitibi and pontiac subprovinces the successor basins were deposited within 100 ma of the majority of the detrital zircon grains primary crystallization ages which is consistent with patterns observed at modern convergent margin settings porcupine assemblage samples contain 5 mesoarchean zircon while pontiac subprovince and timiskaming assemblage samples contain 18 and 13 respectively no local mesoarchean sources exist in the abitibi or pontiac subprovinces suggesting input from an adjacent hinterland the higher proportion of mesoarchean zircon in the timiskaming assemblage relative to the porcupine assemblage suggests that detritus from the hinterland was more prevalent during the later stages of collision probably as a result of progressive uplift and denudation of the hinterland the high proportion of mesoarchean zircon in the pontiac subprovince sedimentary rocks may reflect an additional mesoarchean source comparison to previously published geochronology data for the superior province indicates that the hinterland was to the northwest and is in part composed of the winnipeg river marmion and opatica subprovinces patterns of contractional deformation successor basin formation and felsic plutonism progressively young to the south in the southern superior province and are interpreted in terms of accretionary processes detrital transport across subprovince or terrane boundaries progressive hinterland emergence and foreland directed propagation of the deformational front recorded by successor basins is similar to that observed in modern style collisional or accretionary orogens

geodynamic evolution of the southern abitibi and pontiac terranes evidence from geochemistry of granitoid magma series 2700 2630 ma four distinct granitic series developed during the evolution of the archean abitibi southern volcanic zone svz 1 a minor synvolcanic tonalite trondhjemite granodiorite ttg series was emplaced at 2700 ma which has extremely low k2o 1 5 wt rb 50 ppm and sr 200 ppm higher nb y and sc flat rare earth element ree patterns and negative eu anomalies 2 a voluminous tonalite granodiorite granite quartz monzonite tggm series developed syntectonically at 2695 2685 ma and displays low k2o 1 3 wt rb 10 50 ppm ba 1000 ppm and u enhanced sr depletion of ta nb and ti and strongly fractionated ree patterns la ybn 49 21 3 a late tectonic quartz syenite quartz monzonite granite smg series was emplaced from 2685 to 2675 ma and is grossly similar to the tggm but has lower cao k2o na2o and greater concentrations of rb ba th and u 4 a late tectonic to posttectonic alkali feldspar syenite alkali feldspar quartz syenite ss series was emplaced

geological evolution of the manitouwadge greenstone belt and wawa quetico subprovince boundary superior province ontario constrained by u pb zircon dates of supracrustal and plutonic rocks fifty million years of archean evolution is recorded in the manitouwadge greenstone belt and the wawa quetico boundary region from ca 2720 ma volcanism and subvolcanic plutonism associated with m

the evolution of the southern abitibi greenstone belt in light of precise u pb geochronology this paper summarizes u pb zircon ages for the archean southern abitibi greenstone belt and integrates them together with zircon and baddeleyite data for three new samples into a general framework for the evolution of the region new ages are reported for the ghost range gabbroic complex 2713 super 7 sub 5 ma and for a pyroclastic volcanic rock of the gauthier group 2700 or 3 ma a previously determined age of 2701 super 3 sub 2 ma for the felsic volcanic skead group is confirmed by magmatic zircons from a second sample that also contains a xenocrystic component or 2720 ma indicating that the skead volcano was built on top of an older volcanic sequence the compiled ages show that the southern abitibi greenstone belt developed between 2750 and 2670 ma the earliest ages date remnants of volcanic complexes that occur at the periphery of the belt major preorogenic magmatism was confined mainly to the period 2720 to 2700 ma in general each episode was characterized by the essentially coeval formation of komatiitic tholeiitic and calc alkalic igneous rocks taking into consideration the known geologic geochemical and isotopic data this association is consistent with evolution in paired active are and back are systems older crust was absent from the region but it may have interacted with these arcs and rift systems farther to the west the extensional regime was followed by a period of compression that caused folding and thrusting emplacement of calc alkalic plutons and deposition of turbidites between 2700 and 2688 ma the magmatism became predominantly alkalic during the main timiskaming period between 2681 and 2676 ma this event was accompanied by the deposition of alluvial fluvial sequences and was followed by renewed compression that caused polyphase folding and thrusting probably between approximately 2676 and 2670 ma lamprophyre dikes were associated with these final stages of deformation postorogenic activity includes faulting and episodes of hydrothermal activity locally associated with gold mineralization ages in the range 2630 to 2580 ma for hydrothermal minerals e g titanite and rutile camflo suggest a correlation of these events with lower crustal magmatism and metamorphism as recorded for example in the adjacent kapuskasing zone

structural evolution of a gold bearing transtensional zone within the archean porcupine destor deformation zone southern abitibi greenstone belt eastern ontario canada abstract the garrison camp comprises four structurally distinct orogenic gold deposits that formed in different host lithologies during progressive deformation detailed field mapping drill core logging and geochronological constraints suggest that the 2678 2 ma garrison granitic stock played a fundamental rheological role in the location of the four deposits initial local shear movement occurred along the southwestern margin of the stock leading to the development of the nw trending sinistral ne side up buffonta shear zone which hosts the buffonta deposit subsequently a transtensional zone formed between the ne trending sinistral porcupine destor and munro deformation zones which host the 903 and jonpol deposits respectively finally a local change in shortening orientation from ne to nnw caused westerly directed extension resulting in the formation of the younger gold bearing veins composing the garrcon deposit in situ u pb laser ablation inductively coupled plasma mass spectrometry performed on monazite grains formed within the shear fabric of the munro deformation zone indicates that transtension occurred at 2657 15 ma therefore at least three of the four deposits formed subsequent to crystallization of the garrison granitic stock the reported u pb dates represent the first direct age constraints on the movement along a gold bearing deformation zone in the southern abitibi greenstone belt

hydrothermal alteration zoning and gold concentration at the kerr addison archean lode gold deposit kirkland lake ontario kerr addison a major archcan lode gold deposit of the abitibi belt with a production of approximately 10 x 10 6 oz au approximately 320 metric tons up to 1983 is localized in a zone of talc carbonate and chlorite carbonate rocks immediately south of a regional structural break the kirkland lake larder lake fault zone relict volcanic textures taken in conjunction with the ratios of diag nostic relatively less mobile elements collectively indicate that most of the wall rocks of the mine were originally mafic and ultramafic rocks along with their clastic derivatives regional greenschist facies metamorphism is locally superposed by a distinct zonation of gold associated hydrothermal alteration characterized by massive introduction of co 2 coupled with variable enrichments of alkali metals and calcium which produced systematic trends of alteration mineral assemblages alteration types of the initial stage contain chlorite which is replaced by muscovite or albite in the advanced stage of alteration with a concomitant increase in the proportion of carbonate minerals numerous generations of crosscutting veins are enveloped by alteration borders in which the sequence of the al bearing minerals namely albite mus covite and chlorite develop from the vein to the wall rocks always in a systematic sequence the same sequence is observed at a larger scale from the ore zone to the periphery of the mine area the intensity of alteration can be monitored by saturation indices co 2 ca fe mg for carbonates and 3k na al 3k al and na al for muscovite albite muscovite and albite respectively molar ratios plots of the moving averages of these indices across the 3 850 ft level of the mine reveal a remarkable correspondence to variations of gold abundance suggesting a genetic relationship of gold enrichment to hydrothermal alteration on a broad scale gold is concentrated to the south of the kirkland lake larder lake fault zone and at a more detailed scale in the transition zone between carbonate muscovite and carbonate albite alteration types during advanced alteration fluid x sub co 2 was approximately 0 1 and na k asymp 10 volcanics of the kinojevis and larder lake groups are 18 o enriched relative to pristine tholeiites and possess distinct mineral delta 18 o values probably due to different conditions of marine water alteration during or shortly after extrusion in domains of advanced alteration these are all shifted down to a common narrow bracket here 18 o 16 o and d h data indicate fairly constant temperatures 270 degrees 300 degrees c and a common isotopic composition of hydro thermal fluids delta 18 o 5ppm delta d 30 to 50ppm across the alteration zoning these results are in common with many other archcan lode gold deposits fe dolomite has a uniform delta 13 c value of 2 8 or 0 42 per mil 1sigma throughout the footwall and ore zones but it is enriched by approximately 1 per mil in the graphite free hanging wall rocks fluid delta 13 c value was 4 or 1 per mil reflecting either a magmatic carbon reservoir or mixtures of marine carbonate carbonaceous and magmatic sources the enrichment of gold at one side of the kirkland lake fault zone is interpreted to be the result of development of a metasomatic zoning induced by gradients in oxidation state the precious metal being concentrated in the reducing side zonation of alteration types south of the kirkland lake larder lake fault zone represents various steps of a continuous process of incremental changes of the rocks to adapt to the composition of an externally generated fluid successive generations of fracture arrays and veins have the same alteration patterns and thus the composition of the incoming hydrothermal fluid seems to have remained essentially unchanged through time gold mineralization at the kerr addison mine and its contiguous alteration halo are interpreted to be the result of repeated cycles of hydraulic fracturing fluid penetration and local reaction with rocks fluid rock interaction produced lateral variations of fluid composition which led to gold concentration probably due to gradients in ph preferentially at the interface between the carbonate muscovite and carbonate albite alteration types which is also the site of pyrite concentration the alteration assemblages and specific site of gold pyrite concentration at kerr addison are common to several other described archcan lode gold deposits

rapid dewatering of the crust deduced from ages of mesothermal gold deposits the large scale migration of fluids through the continental crust has been well documented but there is no consensus regarding the timing of fluid migration relative to orogenic episodes or rates of crustal dewatering1 here we present40ar 39ar dates for muscovites from quartz veins along a major shear zone in southeast alaska which show that the veins were emplaced in the early eocene during the late stages of orogenic deformation hydrother mal activity took place for only about 1 myr and along a distance of at least 200 km the fluids were generated by metamorphic reactions in subducted crust along the north american plate margin and were apparently trapped in the crust by the low permeabilities accompanying a convergent tectonic regime until 56 myr ago the rapid dewatering event coincided with a change in plate motion at 56 55 myr which caused a shift from convergent to partly transcurrent tectonics we suggest that this change in tectonic regime led to increased crustal permeabilities and hence the possibility of large scale fluid migration

host rock and structural controls on the nature and timing of gold mineralization at the holloway mine abitibi subprovince ontario the holloway mine a mesothermal gold deposit is located within the western abitibi subprovince ontario mineralized zones that contain microscopic gold within pyrite are hosted by a sequence of metakomatiites mafic to felsic metavolcanic and metasedimentary rocks there were two mineralization events however the early one was the main event in terms of the amount of gold mineralization this event was associated with albitization silicification chloritization and sericitization in addition to pyritization the later mineralization is associated with sericitization and pyritization carbonate and sericite alterations are associated with both mineralizing events results of u pb zircon age dating of rocks within the sequence constrains the main mineralization event to 2672 ma ore lenses of the holloway deposit are enveloped by 080 striking steeply south dipping zones of intense deformation and fabric development within the porcupine destor deformation zone the shear zones are characterized by a strong foliation and locally an associated extension lineation the ore lenses are interpreted to represent lithons that were formed by boudinage of the more competent mineralized zones which are pervasively albitized analysis of geochemical data demonstrates that the ree th nb hf ti fe and al were largely immobile with respect to the albite quartz chlorite sericite and hematite alterations locally preserved textures such as abundant varioles and spherulites indicate that the host metavolcanics were relatively evolved rocks geochemical data show they have an iron enrichment trend typical of tholeiitic mafic to felsic suites and that they were derived through fractional crystallization of parent basalt because of their high fe mg ratios the rocks reacted with hydrothermal solutions carrying gold presumably as thio complexes to form pyrite which scavenged the gold

late archaean thrusting in the northwestern pontiac subprovince canadian shield abstract in the northwestern archaean pontiac subprovince south verging structures such as drag folds with subhorizontal axes stretched objects down dip mineral lineations low angle thrusts and allochthonous metavolcanic slabs were mainly produced by thrusting in response to n s regional compression deformation of the dominantly metasedimentary sequences occurred under barrovian type metamorphism and the horizontal shortening was accompanied by downdip stretching in the regional foliation s1 two nappes are assumed to be present their boundary being marked by an abrupt change in structural style and metamorphic facies two phases of close to isoclinal folding are evident in the upper nappe but are absent from the lower nappe in the upper nappe d2 gives and e w tectonic trend to the rock units f2 folds range from upright to recumbent but are most typically moderately southward inclined folds that plunge gently towards the east or west besides mostly retrograde recrystallization within d2 fault zones s2 is a crenulation cleavage that did not develop sufficiently to obliterate the regional schistosity s1 and its associated stretching and mineral lineations this contrasts with the regionally penetrative nature of the main deformation event d1 and suggests a narrowing or partitioning of high strain zones with time possibly due to a decrease in the regional temperature syn orogenic sedimentation in the northwestern pontiac subprovince was probably enhanced by tectonically controlled uplift resulting from early regional kenoran compression the sedimentary basin was subsequently deformed by further n s compression which led to internal stacking nappe type displacements barrovian metamorphism and thrusting of the southern abitibi over the pontiac subprovince the common style of folding and the same orientation of various structural elements such as cleavage and lineation in the transition zone between the abitibi and pontiac subprovinces indicate continuity in deformation style regional scale transcurrent displacement along the northern subprovince boundary appears as a late localized response to regional compression

observation of shear wave splitting in the multicomponent node data from atlantis field gulf of mexico in 2005 a multicomponent ocean bottom node data set was collected by bp and bhp billiton in the atlantis field in the gulf ofmexico our results are based on data from a few sparse nodes with millions of shots that were analysed as common receiver azimuthal gathers a first order look at p wave arrivals on a common receiver gather at a constant offset reveals variation of p wave arrival time as a function of azimuth indicating the presence of azimuthal anisotropy at the top few layers this prompted us to investigate shear arrivals on the horizontal component data after preliminary processing including a static correction the data were optimally rotated to radial r and transverse t components the r component shows azimuthal variation of traveltime indicating variation of velocity with azimuth the corresponding t component shows azimuthal variation of amplitude and phase polarity reversal the observed shear wave s wave splitting previously observed azimuthal p wave velocity variation and azimuthal p wave amplitude variation all indicate the occurrence of anisotropy in the shallow just below the seafloor subsea sediment in the area from the radial component azimuthal gather we analysed the pp and ps wave amplitude variation for the first few layers and determined corresponding anisotropy parameter and vp vs values since fracture at this depth is not likely to occur we attribute the observed azimuthal anisotropy to the presence of microcracks and grain boundary orientation due to stress the evidence of anisotropy is ubiquitous in this data set and thus it argues strongly in favour of considering anisotropy in depth imaging for obtaining realistic subsurface images at the least

synthesis of the structural evolution and associated gold mineralization of the cadillac fault abitibi canada abstract the cadillac fault zone cfz is a 250 km long east trending crustal discontinuity associated with numerous world class gold deposits in the archean abitibi subprovince in quebec the fault follows the boundary between the abitibi and the pontiac subprovinces and can be divided into four segments 1 rouyn 2 joannes 3 malartic and 4 val d or each displays different attitudes and structural styles the malartic segment strikes se whereas the other segments are e trending abrupt changes in strike or smaller scale faults represent limits between the segments structural styles include four generations of foliation with numerous shear sense indicators and folding specifically related to each foliation structural features can be correlated from one segment to another but display clear variations in attitude or expression a stretching lineation signature is definitely associated with each segment in the malartic segment the predominant e trending schistosity displays an angular relationship with the contact between groups and bedding suggesting that the se trending architecture of this segment was already emplaced prior to ductile deformation the evidence suggests a model where the cfz originates from several independent structures inherited from volcanism prior to timiskaming deformation and abitibi pontiac accretion the proto cfz was then linked up during the timiskaming deposition forming high strain zones inherited structures form the frame on which each deformation event was overprinted with different responses depending on segmentation the structural styles of each segment can be integrated in a structural evolution model for the cfz the n s shortening led to the development of a dominantly e striking penetrative foliation and folding during the subsequent extensional stage the cfz was reactivated with normal kinematics during the pontiac uplift a third deformation event is represented by the local development of nw trending cleavage axial planar to the s shaped minor folds finally a late nw se shortening event produced a dextral strike slip movement with ne striking vertical foliation and development of z shaped folds on bedding surfaces and anterior fabrics linkage of the cfz had a major impact on hydrothermal activity in the southern abitibi as it channeled fluids along large scale pathways distribution of gold bearing intrusions can also be related to segmentation and inherited structures of the cfz this association is expressed by gold mineralization styles present in several longitudinal fields reflecting fault segmentation

using 3d finite difference modeling to design wide azimuth surveys for improved subsalt imaging three dimensional finite difference modeling studies conducted over subsalt structures in the deepwater gulf of mexico confirm the deficiencies of narrow azimuth towed streamer surveys and predict significant improvement in image quality with wide azimuth methods finite difference modeling has provided important design parameters for two separate approaches for wide azimuth surveys ocean bottom receivers distributed in a sparse grid on the ocean floor coupled with a dense grid of source points on the surface and a wide azimuth towed streamer method using multiple seismic vessels in a novel configuration these two methods complement each other ocean bottom receivers may be used effectively where field development has resulted in many obstacles that might interfere with towed streamer methods where the required size of the 3d survey is not too extensive or where very long offsets are required for all azimuths towed streamer methods are more efficient for large surveys and key parameters in the wide

timing of gold mineralization in the val d or district southern abitibi belt evidence for two distinct mineralizing events gold bearing quartz vein deposits in the val d or area of the southern abitibi greenstone belt are classified in two categories based on structural and chronologic relationships young deposits 2690 ma feature commonly deformed orebodies that are cut by dikes of various composition such deposits occur at the siscoe kiena orion and norlartic mines the norlartic main orebody is crosscut by a tonalite dike which has been dated by u pb at 2692 or 2 ma in agreement with structural data these observations show that gold mineralization in the val d or area occurs in at least two different settings and was emplaced at different times

the timmins porcupine gold camp ontario anatomy of an archean greenstone belt and ontogeny of gold mineralization new structural and geochronological data and interpretations from the timmins porcupine gold camp abitibi subprovince more precisely define the stratigraphy and the generation timing and effects of deformation tisdale basalts and porcupine volcaniclastic and turbiditic sedimentary rocks assemblage rocks exhibit three major foliations s2 s3 s4 plus a late constrictional fabric of which s3 and s4 are also present in younger timiskaming assemblage sedimentary rocks pre timiskaming folding has long been recognized in tisdale assemblage rocks but no foliation had previously been attributed to such an event d1 regional uplift and extension produced a low angle unconformity between the tisdale and porcupine assemblages with partial excision of upper tisdale stratigraphy and perhaps of the blake river assemblage d2 involved imbrication of a set of south over north thrust sheets rooted in the porcupine destor deformation zone d3 en echelon folds along the northern flank of the porcupine destor deformation zone are a result of left lateral strike slip along this zone the timiskaming basin lying along the curvilinear trace of the porcupine destor deformation zone formed as a d3 transtensional half graben and the dome fault formed its faulted margin s4 foliation formed during subsequent right lateral strike slip movement and folding of s3 foliation intense d5 constrictional strain deformed earlier lineations as the previously dilatational jog that hosts timiskaming assemblage rocks acted as a compressional jog during right lateral movement along the porcupine destor deformation zone these d2 to d5 phases represent an overall thrusting strike slip transpressional regime there were several phases of gold mineralization in the timmins porcupine gold camp clasts of ankerite veins occur in timiskaming assemblage conglomerate at the dome mine and d3 foliation and folds crosscut early ankerite veining and alteration and some quartz veining thus low grade mineralization and possibly the quartz fuchsite veins predate timiskaming sedimentation however the bulk of gold postdates timiskaming sedimentation quartz carbonate tourmaline gold veins hollinger mcintyre hoyle pond dome aunor delnite mines formed within timiskaming assemblage and tisdale assemblage rocks these gold deposits developed largely as oblique slip and extensional vein arrays formed during north south shortening and local strike slip faulting younger deposits pamour are associated with d4 dip slip faulting and were weakly deformed during late d4 thus the largest known archean lode gold camp formed throughout protracted orogenesis consisting of a broadly transpressional regime with unusually well developed early thrusting

the role of gravity and magma in the structural evolution of a deformed archean volcanic centre timmins ontario canada a deformed bimodal subaqueous volcanic centre in the western archean abitibi subprovince of the canadian shield contains structures comparable with those of relatively undisturbed igneous complexes similarities include an annular fold pattern initiated by structural doming and downsagging of basaltic flows prior to the terminal felsic volcanism during this cycle an ancestral dome was ruptured by a northeasterly regional graben defined by fossil fault scarps preserved beneath the terminal volcanic deposits fissure vents developed along the northwest boundary of the graben gradually drained the underlying magma chamber and transformed the crest of the dome into a central collapse basin surrounded by an annular anticlinal uplift marking the inner periphery of the former dome basalts on the basinward side of the fissure vents became detached along interflow argillites and glided into the central collapse forming secondary gravity folds within the uppermost basalts subaqueous deposition of felsic debris occurred in the graben and subsiding collapse basin succeeded by postvolcanic turbidites the annular folds were modified by two phases of regional deformation separated by an episode of archean molasse sedimentation along the reactivated south boundary of the paleograben

depositional gaps in abitibi greenstone belt stratigraphy a key to exploration for syngenetic mineralization models of greenstone belt development are crucial for exploration allochthonous models predict belts to be a collage of unrelated fragments whereas autochthonous models allow for prediction of syngenetic mineral deposits within specific stratigraphic intervals superior province greenstone belts consist of mainly volcanic units unconformably overlain by largely sedimentary timiskaming style assemblages and field and geochronological data indicate that the abitibi greenstone belt developed autochthonously we describe major revisions to stratigraphy of the abitibi greenstone belt and the implications of an autochthonous development of the volcanic stratigraphy for exploration for syngenetic mineralization the abitibi greenstone belt is subdivided into seven discrete volcanic stratigraphic episodes on the basis of groupings of numerous u pb zircon ages of pre 2750 2750 to 2735 2734 to 2724 2723 to 2720 2719 to 2711 2710 to 2704 and 2704 to 2695 ma we present revised lithotectonic and or stratigraphic nomenclature using these time intervals including 1 isotopic inheritance in younger episodes which indicates that the older episodes 2750 2735 and 2734 2724 ma had greater extent than is presently seen 2 dikes feeding younger volcanic episodes 2706 ma cutting older volcanic units 2734 2724 ma and 3 2710 to 2704 ma mafic to ultramafic sills intruding the 2719 to 2711 ma episode changes to the nomenclature include the identification of pre 2750 ma volcanic episode supracrustal fragments in the northern and southern abitibi greenstone belt and subdivision of the 2719 to 2711 ma 2710 to 2704 ma and 2704 to 2695 ma episodes into lower and upper parts we present the results of this lithostratigraphic subdivision as the first geochronologically constrained stratigraphic and or lithotectonic map of the abitibi greenstone belt many of the volcanic episodes are intercalated with and capped by a relatively thin sedimentary interface zone dominated by chemical sedimentary rocks stratigraphic and geochronological analysis of these zones indicates discontinuous deposition with localized gaps of 2 to 27 m y between volcanic episodes the zones consist of up to 200 m of iron formation chert breccia heterolithic debris flows of volcanic provenance sandstone and or argillite and conglomerate modeling of the time required for deposition of the volcanic units based on rates of magma production in modern arc and plume environments is on the order of 103 to 104 years whereas the time interval between basalt rhyolite cycles is 106 years the sedimentary interface zones are therefore interpreted as condensed sections zones with very low rates of sedimentation in a basinal setting or zones with negligible rates of sedimentation marked by silicification of existing rock types the sedimentary interface zones are therefore considered submarine correlative conformities disconformities or unconformities separating the equivalent of group level stratigraphic and lithotectonic units the unconformity bounded stratigraphic model provides a new regional to deposit scale interpretive model for use in exploration for syngenetic mineralization

structural and stratigraphic controls on magmatic volcanogenic and shear zone hosted mineralization in the chapais chibougamau mining camp northeastern abitibi canada the structure and stratigraphy of the chapais chibougamau mining camp in the archean abitibi greenstone belt of the superior craton quebec canada is reevaluated from new aeromagnetic data geochronology and field studies to provide a framework for syngenetic and epigenetic mineralization mineralization in the chapais chibougamau area is synvolcanic volcanogenic massive sulfide vms synmagmatic fe ti v ni cu au ag cu zn pb veins chibougamau type cu au veins and shear zone hosted including opemiska cu au veins subtype vms deposits occur within felsic volcanic rocks of tholeiitic affinity and mafic to felsic volcanic rocks of transitional to calc alkaline affinity at the top of three volcanic cycles of the roy group vms deposits and early polymetallic veins au ag cu zn pb are associated with nnw to nne striking synvolcanic faults fe ti v deposits occur within the layered zone of the lac dore complex especially where it thickens in areas of interpreted synmagmatic faults subeconomic magmatic ni cu deposits occur at the contacts of mafic ultramafic or tonalitic intrusions chibougamau type cu au veins formed through magmatic hydrothermal processes they are cut by dikes that predate regional d2 deformation but are located within and are deformed by nw and ne trending d2 shear zones shear zone hosted au deposits are developed preferentially within regional e w trending deformation corridors and along nne striking sinistral shear zones while opemiska type cu au veins occur within regional overturned anticlines in mafic sills of the cummings complex u pb dating of detrital zircons provides maximum depositional ages for metasedimentary rocks of the blondeau formation of the roy group and the stella formation of the opemisca group which unconformably overlies the roy group the blondeau formation is 2721 3 ma which is coeval to the age of the windfall member in the urban barry belt both show similar exploration potential as they host early polymetallic au ag cu zn pb veins the stella formation is 2704 2 ma and is unaffected by first generation folds thus providing a time constraint for the earliest folding event d1 this new age also indicates that sedimentation in the chapais chibougamau area occurred earlier than for the timiskaming type assemblages in the southern abitibi greenstone belt but the structural setting and presence of alkaline intrusions suggests similar potential for syenite associated au deposits in the stella formation

evolution of the south central part of the archean abitibi belt quebec part i stratigraphy and paleogeographic model the region comprises parts of the southern zone of the abitibi greenstone belt and of the bellecombe gneiss belt and the belleterre angliers greenstone belt the stratigraphic sequence of the abitibi belt consists of 1 a lower ultramafic division 2 a middle tholeiitic division and 3 an upper diverse division these divisions lap onto an older volcanic sequence to the north and west in the bellecombe belt sediments overlie the lower ultramafic division these sediments coarsen toward the abitibi belt and toward the stratigraphic top the volcanic rocks of the belleterre angliers belt overlie the sediments of the bellecombe belt five paleogeographic phases have been recognized during phase i a deep marine ultramafic lava plain covered the south part of the abitibi belt and the bellecombe belt faulting took place at the duparquet destor break during phase ii tholeiitic basalts formed a deep marine lava plain in the west of the abitibi belt whereas flows erupted mainly from central volcanic c

archean gold bearing quartz veins at the sigma mine abitibi greenstone belt quebec part ii vein paragenesis and hydrothermal alteration the sigma deposit consists of an archean gold bearing vein system in deformed volcanic rocks intruded by two generations of porphyries the veins cut all rock types and wall rock alteration is superposed on greenschist facies metamorphic assemblages there are two related vein sets subvertical veins in ductile shears and subhorizontal veins in extensional fractures between shear zones this paper reports on the paragenesis of extensional veins and related hydrothermal alteration tension veins are composed chiefly of quartz and tourmaline and subordinate amounts of carbonates chlorite pyrite pyrrhotite scheelite and free gold the veins formed by one or more episodes of open space filling the paragenetic sequence consists essentially of successive deposition of carbonate scheelite tourmaline pyrite pyrrhotite carbonate chlorite and quartz most of the gold and tellurides was introduced into fractures and along grain boundaries of recrystallized vein minerals during a postfilling episode of deformation veins are surrounded by zoned alteration envelopes consisting of an outer zone of cryptic alteration characterized by a chlorite carbonate white mica assemblage and an inner zone of visible alteration characterized by a carbonate white mica outer subzone and a carbonate albite inner subzone alteration zones represent reaction fronts advancing into the wall rocks and resulted from progressive interaction of wall rocks with a single hydrothermal fluid the chlorite carbonate white mica zone is characterized by replacement of epidote by calcite and white mica accompanied by fixation of co 2 and k and by release of small amounts of si in carbonate white mica and carbonate albite subzones of visible alteration chlorite biotite and white mica were replaced by calcite albite and quartz variable amounts of gold tourmaline pyrite pyrrhotite and ilmenite were also introduced visible alteration zones are characterized by additions of ca co 2 na b s p and au and by important losses of mg fe al and h 2 o mass balance calculations show that ca na si co 2 s and b in vein minerals were contributed from the hydrothermal fluid whereas fe mg and al were derived from the walls the development of alteration envelopes began with the infiltration of hydrothermal fluids into open extensional fractures and it ceased before complete filling of the veins when continuous mineral coatings formed along vein walls deposition of carbonate accompanied development of cryptic alteration including initial co 2 additions to the wall rocks subsequent deposition of tourmaline pyrite and pyrrhotite carbonate chlorite accompanied the progressive development of visible alteration which encroached on cryptically altered rocks visible alteration is characterized by additions of ca and co 2 to the wall rocks and by release of mg fe and al later bulk quartz deposition which filled the vein openings generally took place after complete development of the alteration envelopes except for this late quartz deposition of vein minerals is attributed to chemical changes in the fluid resulting from progressive wall rock alteration bulk quartz deposition is attributed to progressive cooling of the hydrothermal fluid

evolution of the southern abitibi greenstone belt based on u pb geochronology autochthonous volcanic construction followed by plutonism regional deformation and sedimentation abstract new mapping and u pb zircon geochronological results in the southern abitibi greenstone belt sagb support an autochthonous regional stratigraphy comprised of nine supracrustal assemblages rather than the collage of allochthonous terranes proposed in recent publications based on lithological and geochronological criteria these supracrustal assemblages also encompass the swayze shining tree and montcalm greenstone belts indicating that despite separation by large granitic intrusions they are in fact part of one extensive greenstone belt in conjunction with the mapping the geochronological results support coherent upward facing stratigraphic sections with about 20 of the samples containing inherited zircons with ages similar to those found in underlying assemblages the seven oldest assemblages represent semi continuous volcanism from 2750 to 2697 ma the volcanism is compositionally diverse ranging from komatiite and tholeiitic basalt to calc alkaline mafic to felsic lavas intimate intermingling of the different magma clans occurs throughout much of the stratigraphic section regional fault control on the distribution of the volcanic assemblages provides evidence for early dip slip movement associated with volcanic extension dating back to at least 2725 ma the two youngest assemblages are dominantly sedimentary and were unconformably deposited on the volcanic assemblages in close proximity to regional faults the earlier sedimentary assemblage consists of turbidites and minor iron formation deposited from 2696 to 2692 ma and the youngest one of subaerial conglomerates fluvial sandstones and alkalic to shoshonitic volcanic rocks ranging in age from 2687 to 2675 ma the sedimentary assemblages are broadly contemporaneous with the emplacement of syntectonic granitic plutons regional folding and reactivated movement on the regional faults probably related to accretion of the abitibi to the superior province craton autochthonous repetition of different geodynamic environments over the 50 million years of volcanic activity with five dominantly tholeiitic komatiitic assemblages and two dominantly calc alkaline assemblages as well as the extensive intermingling of these different magma clans in a number of the assemblages appears to be unique to the archean it suggests complex large scale and long lived interaction between mantle plumes and subduction zone magmas the nd isotope data indicate a derivation of the diverse volcanic magmas from homogeneously depleted sources with end 2 5 0 5 demonstrating a lack of contamination by ancient enriched components

time transgressive archean unconformities underlying molasse basin fill successions of dissected oceanic arcs superior province canada abstract late archean diachronous unconformities underlying tectonically controlled coarse clastic successions are located throughout the superior province of canada examples studied in detail include hiatuses at the base of the timmins and kirkland basins in the abitibi greenstone belt and the crowduck and stormy basins in the wabigoon subprovince the timmins molasse basin fill succession overlies a high angle subaerial unconformity separating deepwater turbiditic deposits from fluvial conglomerates a subaerial erosional unconformity defines the contact between mafic flows and overlying felsic volcaniclastic deposits and fluvial conglomerates of the kirkland basin the crowduck and stormy successions are characterized by shallow water and subaerial unconformities between quartz feldspar porphyry stocks and clastic deposits the pronounced characteristics of the molasse basins which include 1 basal unconformities with older sedimentary volcanic or plutonic rocks 2 bounding fault systems 3 ba

stratigraphy and u pb zircon geochronology of kidd creek implications for the formation of giant volcanogenic massive sulphide deposits and the tectonic history of the abitibi greenstone belt within the context of a structural stratigraphic analysis of the giant kidd creek cu zn ag deposit precise u pb zircon ages have been obtained for five critical rock units associated with the deposit massive flow banded footwall rhyolite is dated at 2714 3 1 2 ma slightly younger than a previously published age of 2717 2 ma on nearby rhyolite breccia extrusive rhyolite in the immediate hanging wall to the main ore lenses is dated at 2711 5 1 2 ma leaving an interval of one to several million years for the formation of the deposit we consider the demonstrated longevity of the kidd creek hydrothermal system as a major control on its giant size age constraints together with the size of the deposit suggest a time averaged rate of base metal sulphide deposition of about 10 100 t year peak rates were likely one to possibly two orders of magnitude above time averaged rates hence 100 1000 t year or higher detrital zircon ages on greywackes in the structural footwall to the deposit support structu

u pb zircon geochronology in the southwestern abitibi greenstone belt superior province the abitibi belt is the largest continuous greenstone belt in the superior province of the canadian shield it comprises several composite komatiitic tholeiitic calc alkalic and sedimentary sequences that are folded transected by major faults and intruded by various generations of plutonic rocks precise u pb geochronology has been carried out in the belt for the past decade to solve chronostratigraphic and metallogenetic problems this paper presents new zircon ages and reassesses previously published ones now refined by the addition of abraded and concordant zircon analyses volcanic and subvolcanic units of the timmins area yield the following ages 2727 1 5 ma for a tuff of the upper deloro formation 2703 1 5 ma for a tuff of the upper tisdale formation and 2698 4 ma for the krist fragmental assigned to the top of the tisdale formation the age of a dunite intrusive into the upper deloro formation is revised at 2707 3 ma whereas the aquarius diorite east of timmins yields a poorly define

gold mineralisation throughout about 45 ma of archaean orogenesis protracted flux of gold in the golden mile yilgarn craton western australia the golden mile deposit was discovered in 1893 and represents today the largest archaean orogenic lode gold system in the world 50 m oz produced gold the golden mile deposit comprises three major styles of gold mineralisation fimiston oroya and charlotte styles fimiston style lodes formed at 250 to 350 c and 100 to 200 mpa and are controlled by brittle ductile fault zones their subsidiary fault zone and vein networks including breccias and open cavity infill textures and hydrothermally altered wall rock fimiston lodes were formed late d1 prior to d2 regional upright folding hydrothermal alteration haloes comprise a progression toward the lode of diminishing chlorite an increase in sericite and in fe content of carbonates lodes contain siderite pyrite native gold 17 different telluride minerals au ag tellurides contain 25 of total gold tourmaline haematite sericite and v rich muscovite oroya style lodes formed at similar p t conditions as the fimiston lodes and are controlled by brittle ductile shear zones associated dilational jogs that are particularly well developed at the contact between paringa basalt and black shale interflow sedimentary rocks and altered wall rock the orebodies are characterised by micro breccias and zones of intense shear zone foliation very high gold grades up to 100 000 g t au and the common association of tellurides and vanadian mica green leader oroya lodes crosscut fimiston lodes and are interpreted to have formed slightly later than fimiston lodes as part of one evolving hydrothermal system spanning d1 and d2 deformation ca 2 675 2 660 ma charlotte style lodes exemplified by the mt charlotte deposit are controlled by a sheeted vein stockwork complex of north dipping quartz veins and hydrothermally altered wall rock the mt charlotte orebody formed at 120 to 440 c and 150 to 250 mpa during movement along closely spaced d4 2 625 ma and reactivated d2 faults with the quartz granophyre in the golden mile dolerite exerting a strong lithological control on gold mineralisation veins consist of quartz carbonate minor scheelite and wall rock alteration comprises chlorite destruction and growth of ferroan carbonate sericite pyrite native gold pyrite pyrrhotite is zoned on the scale of vein haloes and of the entire mine giving a vertical temperature gradient of 50 100 c over 1 000 vertical metres the structural hydrothermal model proposed consists of four major stages 1 d1 thrusting and formation of fimiston style lodes 2 d2 reverse faulting and formation of oroya style lodes 3 d3 faulting and dissecting of fimiston and oroya style lodes and 4 d4 faulting and formation of mt charlotte style sheeted quartz vein system the giant accumulation of gold in the golden mile deposit was formed due to protracted gold mineralisation throughout episodes of an archaean orogeny that spanned about 45 ma fluid conduits formed early in the tectonic history and persisted throughout orogenesis with the plumbing system showing a rare high degree of focussing efficiency and duration in addition to the long lasting fluid plumbing system the wide variety of transient structural and geochemical traps multiple fluid sources and precipitation mechanism contributed towards the richest golden mile in the world

geologic and structural setting of gold mineralization in the kirkland lake larder lake gold belt ontario the kirkland lake larder lake gold belt includes the giant kirkland lake and world class kerr addison chesterville gold deposits along with several smaller deposits and occurrences it corresponds to an east trending band of timiskaming clastic and volcanic rocks that unconformably overlie older volcanic assemblages in the southern abitibi greenstone belt of the archean superior province the gold belt is bounded to the south by the larder lake cadillac deformation zone which roughly follows the contact between the younger timiskaming rocks and the older volcanic units three generations of fabrics formed during post timiskaming regional deformation d2 d3 and d4 of the belt north south shortening during d2 produced a penetrative generally east striking steeply dipping s2 foliation and an east plunging l2 stretching lineation s2 is most intense within the syn d2 larder lake cadillac deformation zone and its northeast trending splay the upper canada deformation zone the d2 structures are overprinted by a north trending crenulation cleavage s3 which formed during east west d3 shortening across the belt a northeast trending regional s4 foliation associated with z shaped f4 folds and overprinting both s2 and s3 formed during northwest southeast d4 shortening gold mineralization is localized along the larder lake cadillac deformation zone anoki and mcbean deposits the upper canada deformation zone upper canada deposit and the brittle kirkland lake fault and 04 break kirkland lake deposit the upper canada mcbean and anoki deposits formed during d2 and along with kerr addison chesterville omega and cheminis deposits are probably related to a regionally extensive hydrothermal system associated with the larder lake cadillac deformation zone the sulfide poor gold and telluride bearing quartz veins of the kirkland lake deposit are interpreted to have been emplaced during d4 synchronous with reverse dextral movement along the ore controlling brittle kirkland lake fault the kirkland lake mineralization has a distinct metal signature te au mo pb ag high au ag low as and probably represents a separate hydrothermal system linked to a deep magmatic alkalic fluid source and unrelated to mineralization along the syn d2 deformation zones

mapping spatial variability in shoreline change hotspots from satellite data a case study in southeast australia abstract this study demonstrates how a large scale satellite derived dataset can be used to investigate statistically robust trends in shoreline position over a 31 year period from 1987 to 2017 at a regional scale regional patterns of shoreline behaviour are important for resolving consistent or alternatively dissimilar patterns of past shoreline change such patterns are best explored using temporally frequent and spatially extensive datasets here we analyse satellite derived shorelines to identify spatial patterns of hotspots of coastline change on the wave exposed coast of victoria in south east australia where rates of change exceed 0 5 m yr 1 analysis of shoreline position changes at a 50 m alongshore interval along 900 km of the 1230 km coastline reveals a number of distinct behaviours related to coastal type rock vs sand coast landform shoreline orientation and or anthropogenic drivers of change overall the results show that statistically significant change in shoreline position has affected only a relatively small proportion of the study region over the last 31 years that the proportion and rate of progradational and recessional change is similar and that change is localised but dispersed widely along the victorian coast coasts located at the entrances to large tidal inlets have shown the greatest change the association of hotspots with embayed sandy beaches and adjacent to headlands points to the importance of geological control on shoreline behaviour consistent with other regional scale studies of shoreline change this study found little regional coherence in shoreline behaviour instead change is predominately attributed to local factors such as the geological framework of the coast localised hydrodynamic conditions and anthropogenic influences collectively these results indicate that there is strong geologic control on shoreline erosion in victoria due to the high diversity of landforms along the coastline and that further analysis is required to tease out the seasonal to interannual sensitivities to changes in the historical wave climate and the secondary interaction of sediment supply for headlands and hydrodynamics for tidal inlets

evolution of 3 1 and 3 0 ga volcanic belts and a new thermotectonic model for the hopedale block north atlantic craton canada a new model for evolution of the archean hopedale block based on mapping and supporting u pb geochronological and geochemical studies is highlighted by i ca 3 25 ga emplacement of igneous precursors of maggo gneiss ii g iii emplacement of the hopedale mafic dykes iv 3 1 ga deposition of hunt river volcanic rocks v ca 3 0 ga deposition of florence lake volcanic rocks vi 2 88 2 96 ga greenschist to amphibolite facies fiordian metamorphism and formation of penetrative northeast striking fiordian structures and vii emplacement of a suite of 2 89 2 83 ga tonalite to granite intrusions which partially overlap and locally postdate fiordian metamorphism and deformation the hunt river and florence lake volcanic sequences are different in age but similar in most other respects the former consists mainly of amphibolite facies mafic metavolcanic rocks and lesser amounts of komatiite flows and metasedimentary and 3105

the gold carbonate association source of co2 and co2 fixation reactions in archaean lode deposits abstract abundant carbonate is a ubiquitous feature of archaean lode gold deposits both in domains of alteration enveloping veins and in rocks enclosing auriferous sediments detailed studies of chemical mass balance in metabasalts progressively altered towards gold bearing quartz carbonate veins disposed within shear zones at yellowknife reveal massive additions of co2 k si and fe accompanying mineralisation with concomitant depletions of na coherent behaviour of al sc zr also v and nb provides a reference for constraining the volume relations during hydrothermal alteration in the peripheral regions of alteration depletions of ca and mg result in overall volume reduction but these elements are added to veins and their immediate alteration envelopes where there is a large positive volume change precious metals together with cr ni cu zn pb rb cd and ba have been added to the veins and altered wall rocks whereas quartz noble metals and other trace elements have been precipitated from hydrothermal fluids solution of ca mg and some fe indigenous to peripheral alteration regions combining with co2 from the mineralising reservoir appears to be the process for forming the abundant ferri dolomite gangue observations of many archaean au deposits reveals that carbonate chemistry reflects the nature of wall rocks with wall rocks donating the bivalent metal cations and hydrothermal fluids the co2 alteration reactions at yellowknife involved hydrolysis of albite accompanied by fixation of kaqueous to produce muscovite with na loss and hydrolysis of chlorite epidote with co2 fixation to form ferri dolomite studies of oxygen isotopes fe 2 fe 2 fe 3 and structure reveal that au quartz and carbonate were precipitated in the presence of fluids of probable metamorphic origin 18 o 8 9 at low redox potential and at ambient temperatures of 400 450 c during episodes of hydrofracturing the abundant co2 and k required for extensive carbonate muscovite replacement alteration could be supplied by fluids released during prograde metamorphism under greenschist or greenschist amphibolite facies conditions where the relative proportion of co 2 h 2 o is in the order of 0 2 to 0 5 and k na 1 given high co2 co in the hydrothermal reservoir these molecules may act as complexing agents for transport of au and other rare elements e g w pd ni cr