tectonics fluids and ore deposits mobilization and remobilization abstract the mobilization of metals leading to the formation of many known types of metallic resource involves the focussed flow of very large km 3 fluid volumes different types of fluids such as sea water and metamorphic and meteoric fluids with or without biomolecules may be specific for certain metals or suites of metals where large fluid volumes are part of a geologic process there is potential for local metal enrichment examples of such processes within the context of plate tectonics include convective flow of sea water at ocean ridges in relation to ophiolite cu zn mineralization and black smokers subduction of metal enriched sediments and the tectonic recycling of sn w mineralization metamorphic dewatering of subducted oceanic crust in the context of au deposits metamorphic degassing around high level granitic plutons and metamorphic re equilibration of the underthrust plate in relation to continental thrusting in addition during weathering processes short term leaching produces fertile soils whereas long term leaching can result in lateritic ores the large scale remobilization of ore deposits or of mineralization where metal enrichment is currently sub economic is improbable unless large fluid volumes are involved or the crust undergoes major tectonic re arrangement but it is perhaps possible that these situations are more common than we suppose and that such multistage events are indicated by the long term persistence of metallogenic provinces

applications of texture attribute analysis to 3d seismic data in this study texture attribute analysis application to 3d surface seismic data is presented this is done by choosing a cubic texel texture element from the seismic data to generate a gray level occurrence matrix which in turn is used to compute second order statistical measures of textural characteristics the cubic texel is then successively made to glide through the 3d seismic volume to transform it to a plurality of texture attributes application of texture attributes to two case studies from alberta confirm that these attributes enhance understanding of the reservoir by providing a clearer picture of the distribution volume and connectivity of the hydrocarbon bearing facies in the reservoir

curie surface of borborema province brazil abstract the curie surface interpreted from magnetic data through spatial frequency domain techniques is used to provide information on the thermal structure of borborema province the borborema province is part of the neoproterozoic collision of an orogenic system situated between the sao francisco congo and sao luis west africa cratons which formed the gondwana supercontinent the curie surface of borborema province varies from 18 to 59 km which reveals the complexity in the crustal composition of the study area the thermal structure shows different crustal blocks separated by the main shear zones which corroborates the evolution model of allochthonous terranes the curie surface signature for the west portion of pernambuco shear zone may indicate processes of mantle serpentinization once the curie isotherm is deeper than mohorovic discontinuity in this region the amplitude of bouguer anomaly decreases which corroborates long wavelength anomaly observed in the magnetic anomaly we interpreted this pattern as evidence of the brasiliano pan africano s subduction collision event earthquakes in the region are concentrated mainly in shallow curie surface regions less resistant crust and in transition zones between warm and cold blocks we calculated the horizontal gradient of the curie depth to emphasize the signature of contact between the thermal blocks these regions mark possible crustal discontinuities and have high correlation with orogenic gold occurrence in the study area

vs30 and spectral response from collocated shallow active and passive source vs data at 27 sites in puerto rico shear wave velocity vs and time averaged shear wavevelocity to 30 m depth vs30 are the key parameters used in seismic site response modeling and earth quake engineering design where vs data are limited available data are often used to develop and refine map based proxy models of vs30 for predicting ground motion intensities in this paper we present shallow vs data from 27 sites in puerto rico these data were acquired using a multimethod acquisition approach consisting of noninvasive collocated active source body wave refraction reflection active source surface wave at nine sites and passive source surface wave refraction micro tremor remi techniques vs versus depth models are constructed and used to calculate spectral response plots for each site factors affecting method reliability are analyzed with respect to site specific differences in bedrock vs and spectral response at many but not all sites body and surface wave methods generally determine similar depths to bedrock and it is the difference in bedrock vs that influences site ampli fication the predicted resonant frequencies for the majority of the sites are observed to be within a relatively narrow bandwidth of 1 3 5 hz for a first order comparison of peak frequency position predictive spectral response plots from eight sites are plot ted along with seismograph instrument spectra derived from the time series of the 16 may 2010 puerto rico earthquake we show how a multimethod acquisition approach using collocated arrays compliments and corroborates vs results thus adding confi dence that reliable site characterization information has been obtained

the role of vegetation in the formation of anabranching channels in an ephemeral river northern plains arid central australia as the distribution and abundance of vegetation in drylands is often controlled by the greater availability of water along river channels riparian vegetation has the potential to influence significantly dryland river form process and behaviour this paper demonstrates how a small indigenous shrub the inland teatree melaleuca glomerata influences the formation and maintenance of anabranching channels in a reach of the ephemeral marshall river northern plains arid central australia here the marshall is characterized by ridge form anabranching where water and sediment are routed through subparallel multiple channels of variable size which occur within a typically straight channel train channels are separated by channel train ridges narrow flow aligned vegetated features or by wider islands by providing a substantial element of boundary roughness dense stands of teatrees growing on channel beds or atop the ridges and islands influence flow velocities flow depths and sediment transport resulting in flow diversion bank and floodplain erosion and especially sediment deposition ridges and islands represent a continuum of forms and their formation and development can be divided into a three stage sequence involving teatree growth and alluvial sedimentation 1 teatrees colonize a flat sandy channel bed initiating the formation of ridges by lee side accretion individual ridges grow laterally vertically and longitudinally and maintain a geometrically similar streamlined lemniscate form that presents minimum drag 2 individual ridges grow in size and interact with neighbouring ridges causing the lemniscate forms to become distorted ridges in the lee of other ridges tend to be protected from the erosive effects of floods and survive whereas individual teatrees or small ridges exposed to flow concentrated between larger ridges tend to be removed 3 ridges lengthen and coalesce with downstream ridges eventually subdividing the channel train into well defined anabranches this sequence turns a channel initially obstructed with dense and chaotic stands of teatrees into a well organized system of ridge form anabranches in the moderate to low gradient marshall river which is colonized by an abundance of within channel vegetation and subject to declining downstream discharges this helps to minimize flow resistance thereby maintaining an efficient water and sediment flux copyright 2000 john wiley sons ltd

u pb single zircon pb evaporation and sm nd isotopic study of a granulite domain in se madagascar madagascar is a poorly known precambrian domain at the eastern border of the mozambique belt strongly affected by the pan african orogeny this large island represents a key part of gondwanaland and the accurate dating of the major metamorphic event is critical for the reconstruction of that supercontinent in the southeastern zone of the island metamorphism has reached high temperature and low pressure conditions 850 c and 5 kbar with moderate retrogression a u pb conventional multigrain single zircon stepwise pb evaporation and sm nd geochronological study on meta felsic rocks has shown that basement of at least lower proterozoic age was strongly metamorphosed around 570 580 ma this tectometamorphic event nearly obliterated any pre pan african zircon isotopic memory the granulite facies metamorphism is associated with the syn metamorphic emplacement of the anosyan charnock ites and granites a strong channelized fluid contribution at 545 ma has produced the re crystallization of biotite apatite

late neoproterozoic cambrian granitic magmatism in the aracuai orogen brazil the eastern brazilian pegmatite province and related mineral resources

unsupervised seismic facies analysis using wavelet transform and self organizing maps unsupervised seismic facies analysis provides an effective way to estimate reservoir properties by combining different seismic attributes through pattern recognition algorithms however without consistent geological information parameters such as the number of facies and even the input seismic attributes are usually chosen in an empirical way in this context we propose two new semiautomatic alternative methods in the first one we use the clustering of the kohonen self organizing maps soms as a new way to build seismic facies maps and to estimate the number of seismic facies in the second method we use wavelet transforms to identify seismic trace singularities in each geologically oriented segment and then we build the seismic facies map using the clustering of the som we tested both methods using synthetic and real seismic data from the namorado deepwater giant oilfield in campos basin offshore brazil the results confirm that we can estimate the appropriate number of seismic facies through the clustering of the som we also showed that we can improve the seismic facies analysis by using trace singularities detected by the wavelet transform technique this workflow presents the advantage of being less sensitive to horizon interpretation errors thus resulting in an improved seismic facies analysis

integrated seismic texture segmentation and cluster analysis applied to channel delineation and chert reservoir characterization in recent years 3d volumetric attributes have gained wide acceptance by seismic interpreters the early introduction of the single trace complex trace attribute was quickly followed by seismic sequence attribute mapping workflows three dimensional geometric attributes such as coherence and curvature are also widely used most of these attributes correspond to very simple easy to understand measures of a waveform or surface morphology however not all geologic features can be so easily quantified for this reason simple statistical measures of the seismic waveform such as rms amplitude and texture analysis techniques prove to be quite valuable in delineating more chaotic stratigraphy in this paper we coupled structure oriented texture analysis based on the gray level co occurrence matrix with self organizing maps clustering technology and applied it to classify seismic textures by this way we expect that our workflow should be more sensitive to lateral changes rather than vertical changes in ref

salt body detection from seismic data via sparse representation in seismic interpretation and seismic data analysis it is of critical importance to effectively identify certain geologic formations from very large seismic data sets in particular the problem of salt characterization from seismic data can lead to important savings in time during the interpretation process if solved efficiently and in an automatic manner in this work we present a novel numerical approach that is able to automatically segmenting or identifying salt structures from a post stack seismic data set with a minimum intervention from the interpreter the proposed methodology is based on the recent theory of sparse representation and consists in three major steps first a supervised learning assisted by the user which is performed only once second a segmentation process via unconstrained 1 optimization and finally a post processing step based on signal separation furthermore since the second step only depends upon local information at each time the whole process greatly benefits from parallel computing platforms we conduct numerical experiments in a synthetic 3d seismic data set demonstrating the viability of our method more specifically we found that the proposed approach matches up to 98 53 with respect to the corresponding 3d velocity model available in advance finally in appendixes a and b we present a convergence analysis providing theoretical guarantees for the proposed method

digital image processing techniques for enhancement and classification of seamarc ii side scan sonar imagery the recent growth in the production rate of digital side scan sonar images coupled with the rapid expansion of systematic seafloor exploration programs has created a need for fast and quantitative means of processing seafloor imagery computer aided analytical techniques fill this need a number of numerical techniques used to enhance and classify imagery produced by seamarc ii a long range combination side scan sonar and bathymetric seafloor mapping system are documented three categories of techniques are presented 1 preprocessing corrections radiometric and geometric 2 feature extraction and 3 image segmentation and classification an introduction to the concept of feature vectors is provided along with an explanation of the method of evaluation of a texture feature vector based upon gray level co occurrence matrices glcm an alternative to the a priori texel texture element subdivision of images is presented in the form of region growing and texture analysis regata this routine provides a texture map of spatial resolution superior to that obtainable with arbitrarily assigned texel boundaries and minimizes the possibility of mixed texture signals due to the combination of two or more textures in an arbitrarily assigned texel computer classification of these textural features extracted via the glcm technique results in transformation of images into maps of image texture these maps may either be interpreted in terms of the theoretical relationships shown between texture signatures and wavelength or converted to geologic maps by correlation of texture signatures with ground truth data these techniques are applied to seamarc ii side scan sonar imagery from a variety of geologic environments including lithified and nonlithified sedimentary formations volcanic and sedimentary debris flows and crystalline basaltic outcrops application of the above processing steps provided not only superior images for both subjective and quantitative analysis but also the critical ability to discriminate between outcrops with distinct lithologies but similar image intensity

transamazonian orogeny in the southern sao francisco craton region minas gerais brazil evidence for paleoproterozoic collision and collapse in the quadrilatero ferrifero abstract the paleoproterozoic transamazonian orogeny yielded a series of discrete orogens in brazil the present field study in the quadrilatero ferrifero qf indicates that the southern sao francisco craton region of the brazilian highlands preserves a portion of one of these orogens two sets of transamazonian structures occur in this region the first consists of northwest verging folds and thrusts affecting supracrustal sequences it is suggested that this set formed in a fold thrust belt setting shortly after 2 125 ga during the closure of a passive margin basin that had initiated along the margins of a preexisting continental mass at ca 2 5 ga the second set consists of structures defining the prominent dome and keel architecture of the qf this set a consequence of the emplacement of basement domes against supracrustal rocks at 2 095 ga may reflect the consequences of orogenic collapse narrow conglomerate filled intermontane basins may have formed coevally with dome emplacement formation of an ocean basin east of the present day sao francisco craton eventually occurred in late mesoproterozoic in effect the transamazonian orogen of the qf represents the collision and collapse stages of a paleoproterozoic wilson cycle the contractional phase of the transamazonian orogeny probably represents accretion of an offshore arc to the eastern and southeastern margin of the present day sao francisco craton region the arc and an associated suture may be traced in the brasiliano pan african orogen east of the sao francisco craton northwards into the northeastern lobe of the sao francisco craton clearly initial assembly of crustal blocks to form a larger continent involving south america occurred during the paleoproterozoic 2 1 ga post transamazonian rifting of this continent created the basins which were later inverted during the brasiliano assembly of gondwana

seismic texture analysis for reservoir prediction and characterization a plethora of seismic attributes are currently in use for reservoir prediction and characterization some are useful in understanding subsurface stratigraphy like channels while others are useful for structural interpretation anticlines faults fractures etc volumetric computation of seismic attributes is helpful to interpreters for 3d seismic visualization and interpretation in addition to the time of a seismic reflection resulting in a time structure map the more commonly used seismic attributes are rms amplitude frequency coherence avo and impedance these attributes are based on clearly established morphological or petrophysical models with some attributes sensitive to rock types some to fluid saturation some to porosity and some to minor faults or fractures within the reservoir our case study of a diagenetically altered mississippian limestone resulting in complex paleo topography defies simple analysis even with adequate well control and good ties to 3d seismic data uncertainty in

3d geological modeling for prediction of subsurface mo targets in the luanchuan district china abstract three dimensional 3d district scale geoscience information for the luanchuan mo district was integrated for understanding the development of its regional geology and ore forming processes and for decision making about potential targets for mineral exploration the methodology and datasets used were 1 construction of an initial geological model 25 km 20 km 2 5 km using 1 10 000 scale geological map nine geological cross sections and gravity and magnetic data 2 construction of three large scale mo deposits model 5 km 4 km 2 5 km using 1 2000 scale geological and topographic maps 288 boreholes total core length of 158 700 m and 32 1 2000 scale cross sections 3 3d inversion of 1 25 000 scale gravity and magnetic data for identification metallogenic anomaly zones which are associated with jurassic intrusions 4 extraction of ore controlling formation and sequence of the luanchuan group using the large scale 3d models of mo deposits and results of analysis of lithogeochemical samples from outcrops and borehole cores 5 identification of ore forming and ore controlling faults using the large scale 3d model of mo deposits and mineralized jurassic granite porphyry stocks 6 boost weights of evidence and concentration volume c v fractal analyses to integrate metallogenic information and to identify and classify potential mo targets four classes of exploration targets were identified using c v modeling and 3d known orebodies model the first and second class targets are mainly located in three large magma skarn type deposit camps occupying 1 4 km3 with total estimated reserve of 2 3 mt the third class targets which are mainly located in huangbeiling and yuku deposit camps comprising concealed magma skarn type deposits occupy 2 8 km3 and represent a new target exploration zone in the luanchuan district the fourth class targets which are located in the huoshenmiao majuan and daping zones occupy 15 km3 and represent potential mineral resources with likely similar orebody features as the yuku deposit

an introduction to chert reservoirs of north america jim rogers has been studying mid continent and rocky mountain hydrocarbon reservoirs for 46 years often concentrating on pennsylvanian and mississippian carbonate rocks and cherts after graduate school at the university of michigan jim spent 15 years at the shell university studying with mentors r n ginsburg e a shinn r h nanz and h a bernard and prospecting in kansas and north dakota in 1970 he began conducting independent regional reservoir studies with several associates these studies were incorporated into his national geological services inc in 1979 jim continues to search for and write about prospective reservoirs while serving in various editorial positions and teaching geology in the caribbean mark w longman is a consulting geologist who specializes in the study of carbonate rocks and reservoirs he has worked on a wide variety of projects ranging from specific core and petrographic studies on individual hydrocarbon reservoirs and wells to regional studies covering entire basins states and countries his specialties include interpretation of carbonate depositional facies and diagenesis and tying these interpretations to wire line logs he received a b a degree from albion college michigan in 1972 and a ph d from the university of texas at austin in 1976 before becoming a consultant in 1984 he was a research geologist with cities service company s research laboratory in tulsa and later worked with coastal oil and gas corporation and buttercup energy in denver this volume represents part of the current work of more than 20 earth scientists who have studied hydrocarbon reservoirs in chert some in the petroleum industry will be surprised that many trillions of cubic feet of natural gas and hundreds of millions of barrels of oil have been and will be produced from these strange rocks despite this remarkable fact the literature on hydrocarbons and pore space in chert reservoirs is

lithospheric controls on the formation of provinces hosting giant orogenic gold deposits ages of giant gold systems 500 t gold cluster within well defined periods of lithospheric growth at continental margins and it is the orogen scale processes during these mainly late archaean palaeoproterozoic and phanerozoic times that ultimately determine gold endowment of a province in an orogen a critical factor for giant orogenic gold provinces appears to be thickness of the subcontinental lithospheric mantle sclm beneath a province at the time of gold mineralisation as giant gold deposits are much more likely to develop in orogens with subducted oceanic or thin continental lithosphere a proxy for the latter is a short pre mineralisation crustal history such that thick sclm was not developed before gold deposition in constrast orogens with protracted pre mineralisation crustal histories are more likely to be characterised by a thick sclm that is difficult to delaminate and hence such provinces will normally be poorly endowed the nature of the lithosphere also influences the intrinsic gold concentrations of potential source rocks with back arc basalts transitional basalts and basanites enriched in gold relative to other rock sequences thus segments of orogens with thin lithosphere may enjoy the conjunction of giant scale fluid flux through gold enriched sequences although the nature of the lithosphere plays the crucial role in dictating which orogenic gold provinces will contain one or more giant deposits the precise siting of those giants depends on the critical conjunction of a number of province scale factors such features control plumbing systems traps and seals in tectonically and lithospherically suitable terranes within orogens

application of multi seismic attributes analysis in the study of distributary channels abstract during the exploration of stratigraphic reservoirs the key to locating these reservoirs is to identify the sandstone distribution seismic data can be used to recognize large scale distributary channel sedimentary bodies however depiction of sedimentary bodies in small distributary channels using traditional interpretation data from seismic profiles is extremely difficult in the upper cretaceous first sandstone bed of the third member of the nenjiang formation called the nen 3 member for simplicity in the xb area of the southern songliao basin distributary channels are the main sedimentary facies the distributary channels migrate frequently therefore it is difficult to precisely depict the morphology of the channel and the distribution of sandstone in this study we investigated the deposition of distributary channels using equal scale formation plane seismic attributes such as post stack amplitude instantaneous amplitude and seismic waveform classification analyzed well logging data from target formations and mapped the distribution of distributary channels this study shows that seismic sedimentological study and stacking multiple attribute analysis can identify the distribution of distributary channels precisely and effectively the attributes of equal scale strata slices are evidently superior to those of time and horizon slices attribute extraction and selection of equal scale formation slices is an essential step the comprehensive selection of seismic attributes that show a good correlation to a single well can be used to clearly depict channel bodies the overlap of the 40 hz single frequency energy and the rms amplitude depicts the sedimentary characteristics and shapes of sandstone bodies in main channels as well as small scale distributary channels more clearly than a single attribute these attributes show that the first sandstone bed of the nen 3 member was from distributary channels with complex shapes the distributary channels cut across each other vertically and laterally it indicates that during the deposition of the nen 3 member in xb area the direction of the main channel is from north to south and the provenance could be from north and east the method of this paper may provide some helpful suggestions to the geologist using seismic attributes to undertake research on sedimentary environment at other places in the world

geologic provinces of oklahoma the geologic provinces of oklahoma are mainly the product of tectonics and attendant sedimentation of pennsylvanian age most boundaries are structural thus the provinces map is a generalized tectonic map permian and post paleozoic strata tend to mask those structures but most of those strata have been removed by erosion except in the anadarko basin and the wichita uplift provinces the location of most of oklahoma s oil and gas resources are either influenced by or are the direct result of pennsylvanian tectonics and sedimentation patterns therefore the present study also defines provinces in the subsurface on the basis of geological criteria the authors have attempted to use the originally published names for the recognized provinces however we also have used the most geologically correct names i e we recommend abandonment of the term nemaha ridge because it is not a geologic term nor does it describe the feature accurately

predictive painting of 3d seismic volumes predictive painting is a numerical algorithm that spreads information in 3d volumes according to the local structure of seismic events the algorithm consists of two steps first local spatially variable inline and crossline slopes of seismic events are estimated by the plane wave destruction method next a seed trace is inserted in the volume and the information contained in that trace is spread inside the volume thus automatically painting the data space immediate applications of this technique include automatic horizon picking and flattening in applications to both prestack and poststack seismic data analysis synthetic and field data tests demonstrate the effectiveness of predictive painting

the archean bif hosted lamego gold deposit rio das velhas greenstone belt quadrilatero ferrifero evidence for cambrian structural modification of an archean orogenic gold deposit abstract the lamego orogenic gold deposit 1 3 mt measured resources at 7 26 g t au is located at the south western end of the 5 km long cuiaba lamego trend quadrilatero ferrifero region brazil both archean orogenic gold deposits are situated in the rio das velhas greenstone belt with the lithological succession at lamego consisting of metamorphosed greenschist facies mafic volcanic rock chert and banded iron formation bif and carbonaceous and micaceous pelites the lamego fold which controls the lamego deposit is the most visible structure related to the d1 d2 event with a perimeter of about 4 8 km and a maximum width of 450 m the fold is defined by the layering of the mafic unit with minor bif and large exposures of carbonaceous and micaceous pelites it is a rootless reclined isoclinal cylindrical fold with an axial trace striking northwest southeast dipping 20 to 30 the hinge zone is thickened and the limbs are thinned with the limbs dipping 20 to 30 to the se orebodies consist of the lamego bif where gold mineralized zones are related to iron rich bands and associated silicification zones replacement style mineralization is associated with sulfide bands mainly pyrite as rich pyrite and arsenopyrite two structural generations g1 and g2 are recognized and encompass a set of structural elements the g1 structural generation developed in a progressive deformation event and resulted in structures oriented from ne to sw and dipping to the se structures pertaining to the g2 structural generation are oriented n s dipping to the w the four major high grade gold orebodies are carruagem queimada arco da velha and cabeca de pedra their gold grade shows a spheroidal pattern and a distribution that varies along the s1 2 foliation these lenses represent the hinge zone of f2 reclined folds with the plunge of the orebodies controlled by the f2 fold axes the lower grade gold lenses are controlled by pinch and swell and locally expressed quartz boudins developed during d1 d2 they have two orthogonal directions one to the nw se and the other to the ne sw thereby defining chocolate tablet style boudinage hydrothermal monazite grains in a mineralized mafic volcanic rock indicate that mineralization formed at 2730 42 ma u pb shrimp younger monazite dated at 2387 46 ma and xenotime dated at 518 5 9 ma suggest siderian and cambrian imprint in the lamego deposit area the cambrian age reflects the late stages of the brasiliano orogenic cycle which is expressed in the lamego deposit by the s3 crenulation cleavage trend ns and dip steeply to the e importantly the cambrian structural modification is responsible for the present geometry of the lamego orebodies but is not associated with hydrothermal alteration it has not introduced any new gold and also has not caused remobilization of the orebodies or ore minerals

texture attribute analysis of gpr data for archaeological prospection we evaluate the applicability and the effectiveness of texture attribute analysis of 2 d and 3 d gpr datasets obtained in different archaeological environments textural attributes are successfully used in seismic stratigraphic studies for hydrocarbon exploration to improve the interpretation of complex subsurface structures we use a gray level co occurrence matrix glcm algorithm to compute second order statistical measures of textural characteristics such as contrast energy entropy and homogeneity textural attributes provide specific information about the data and can highlight characteristics as uniformity or complexity which complement the interpretation of amplitude data and integrate the features extracted from conventional attributes the results from three archaeological case studies demonstrate that the proposed texture analysis can enhance understanding of gpr data by providing clearer images of distribution volume and shape of potential archaeological targets and related stratigraphic units particularly in combination with the conventional gpr attributes such strategy improves the interpretability of gpr data and can be very helpful for archaeological excavation planning and more generally for buried cultural heritage assessment

lithofacies associations and structural evolution of the archean rio das velhas greenstone belt quadrilatero ferrifero brazil a review of the setting of gold deposits abstract the rio das velhas greenstone belt is located in the quadrilatero ferrifero region in the southern extremity of the sao francisco craton central southern part of the state of minas gerais se brazil the metavolcano sedimentary rocks of the rio das velhas supergroup in this region are subdivided into the nova lima and maquine groups the former occurs at the base of the sequence and contains the major au deposits of the region new geochronological data along with a review of geochemical data for volcanic and sedimentary rocks suggest at least two generations of greenstone belts dated at 2900 and 2780 ma seven lithofacies associations are identified from bottom to top encompassing 1 mafic ultramafic volcanic 2 volcano chemical sedimentary 3 clastic chemical sedimentary 4 volcaniclastic association with four lithofacies monomictic and polymictic breccias conglomerate graywacke graywacke sandstone graywacke argillite 5 resedimented association including three sequences of graywacke argillite in the north and eastern at greenschist facies and in the south at amphibolite metamorphic facies 6 coastal association with four lithofacies sandstone with medium to large scale cross bedding sandstone with ripple marks sandstone with herringbone cross bedding sandstone siltstone 7 non marine association with the lithofacies conglomerate sandstone coarse grained sandstone fine to medium grained sandstone four generations of structures are recognized the first and second are archean and compressional driven from nne to ssw the third is extensional and attributed to the paleoproterozoic transamazonian orogenic cycle and the fourth is compressional driven from e to w is related to the neoproterozoic brasiliano orogenic cycle gold deposits in the rio das velhas greenstone belt are structurally controlled and occur associated with hydrothermal alterations along archean thrust shear zones of the second generation of structures sedimentation occurred during four episodes cycle 1 is interpreted to have occurred between 2800 and 2780 ma based on the ages of the mafic and felsic volcanism and comprises predominantly chemical sedimentary rocks intercalated with mafic ultramafic volcanic flows it includes the volcano chemical sedimentary lithofacies association and part of the mafic ultramafic volcanic association the cycle is related to the initial extensional stage of the greenstone belt formation with the deposition of sediments contemporaneous with volcanic flows that formed the submarine mafic plains cycle 2 encompasses the clastic chemical sedimentary association and distal turbidites of the resedimented association in the eastern sector of the quadrilatero ferrifero it was deposited in the initial stages of the felsic volcanism cycle 2 includes the coastal and resedimented associations in the southern sector in advanced stages of subduction in this southern sedimentary cycle it is also possible to recognize a stable shelf environment following the felsic volcanism cycle 3 comprises sedimentary rocks of the volcaniclastic and resedimented lithofacies associations largely in the northern sector of the area the characteristics of both associations indicate a submarine fan environment transitional to non marine successions related to felsic volcanic edifices and related to the formation of island arcs cycle 4 is made up of clastic sedimentary rocks belonging to the non marine lithofacies association they are interpreted as braided plain and alluvial fan deposits in a retroarc foreland basin with the supply of debris from the previous cycles