La Mine Colombia, située dans le District Aurifère d'El Callao, Venezuela, est considérée comme un gisement de type "géant" (i.e. > 500 t Au) car les réserves prouvées sont égales à 23 millions d'onces (= 740 t Au), ce qui fait de ce gisement le plus gros gisement du Craton Guyanais. La minéralisation est encaissée dans des formations basaltiques d'âge paléoprotérozoïque présentant toutes les caractéristiques des basaltes de plateau océanique. La minéralisation se localise au niveau de trois filons sécants sur la foliation, appelés "veine de quartz aurifère Colombia, América et Hansa". Ces "veines" sont en fait constituées par un réseau interconnecté de veines de quartz mais aussi d'ankérite et d'albite, délimitant une caisse filonienne, qui peut être définie par un mur et un toit, dans laquelle le réseau de veines englobe de nombreux fragments de basalte fortement pyritisés. L'or se rencontre quasi-systématiquement dans les fragments de métabasalte, en relation étroite avec la pyrite. Nous considérons ces systèmes de veines comme des "corridors" de déformation minéralisés, qui se seraient formés dans le domaine de transition fragile-ductile, en présence d'un même fluide hydrothermal à H2O-CO2-NaCl et à faible salinité. Ces corridors minéralisés, se formeraient en relation avec une succession de microséismes, à chaque microséisme, une nouvelle génération de pyrite cristalliserait dans les fragments de basalte. Cette pyrite renfermerait systématiquement de l'or soit en substitution dans le réseau cristallin du cristal, soit sous forme de nano-inclusions de sulfosels polymétalliques ; cet or " invisible " représenterait l'or primaire du gisement. De ce fait, nous considérons que l'essentiel de l'or "visible" du gisement serait secondaire et le produit de la remobilisation de l'or primaire "invisible". Nous considérons que cet événement tardif de déformation dans l'orogenèse Transamazonienne est primordial pour avoir des grains d'or visibles et donc un gisement économiquement exploitable.

Geologically-constrained inversion of geophysical data is a powerful method for predicting geology beneath cover. The process seeks 3D physical property models that are consistent with the geology and explain measured geophysical responses. The recovered models can guide mineral explorers to prospective host rocks, structures, alteration and mineralisation. This thesis provides a comprehensive analysis of how the University of British Columbia Geophysical Inversion Facility (UBC–GIF) gravity and magnetic inversions can be applied to subsurface mapping and exploration by demonstrating the necessary approach, data types, and typical results. The non-uniqueness of inversion demands that geological information be included. Commonly available geological data, including structural and physical property measurements, mapping, drilling, and 3D interpretations, can be translated into appropriate inversion constraints using tools developed herein. Surface information provides the greatest improvement in the reliability of recovered models; drilling information enhances resolution at depth. The process used to prepare inversions is as important as the geological constraints themselves. Use of a systematic workflow, as developed in this study, minimises any introduced ambiguity. Key steps include defining the problem, preparing the data, setting inversion parameters and developing geological constraints. Once reliable physical property models are recovered they must be interpreted in a geological context. Where alteration and mineralisation occupy significant volumes, the mineralogy associated with the physical properties can be identified; otherwise a lithological classification of the properties can be applied. This approach is used to develop predictive 3D lithological maps from geologically-constrained gravity and magnetic inversions at several scales in the Agnew-Wiluna greenstone belt in Australia’s Yilgarn Craton. These maps indicate a spatial correlation between thick mafic-ultramafic rock packages and gold deposit locations, suggesting a shared structural control. The maps also identify structural geometries and relationships consistent with the published regional tectonic framework. Geophysical inversion provides a framework into which geological and geophysical data sets can be integrated to produce a holistic prediction of the subsurface. The best possible result is one that cannot be dismissed as inconsistent with some piece of geological knowledge. Such a model can only be recovered by including all available geological knowledge using a consistent workflow process.

Le bouclier Est Antarctique est constitué de nombreux domaines géologiques accrétés autour de 530 Ma. Tous ces domaines enregistrent la trace des événements Grenvillien et Pan-Africain à l'exception d'un seul : le Craton de Terre Adélie. <br />Le Craton de Terre Adélie et son prolongement septentrional, le Craton du Gawler (en South Australia), font partie d'un même bloc : le Mawson Continent. Ils présentent donc une histoire géologique commune avant l'ouverture du domaine océanique Austral il y a environ 90 Ma. Ces cratons sont constitués d'un socle métamorphique polyphasé formé et structuré lors de deux événements géologiques majeurs datés au Néoarchéen (∼ 2.5 Ga) et au Paléoprotérozoïque (∼ 1.7 Ga). <br />Cette étude présente les mécanismes tectoniques à l'origine de la structuration de ce paléo-continent. Les campagnes de terrain et les travaux en laboratoire (pétrologie, géochronologie Ar–Ar et U–Th–Pb) réalisés sur des roches provenant des deux cratons ont permis (1) de préciser l'âge et l'origine de la déformation néoarchéenne ainsi que le comportement de la lithosphère continentale à cette époque et (2) de quantifier l'importance de la déformation paléoprotérozoïque au sein du noyau archéen et dans les domaines paléoprotérozoïques adjacents. <br />Ces travaux apportent de nouvelles contraintes sur la tectonique précambrienne. <br />Nos travaux ont permis de mettre en évidence et de modéliser numériquement en 3D l'évolution à l'échelle lithosphérique de la déformation lors de l'affaiblissement des contraintes tectoniques convergentes appliquées à une lithosphère archéenne chaude. Sous l'influence de la gravité, la lithosphère chaude va fluer dans une direction perpendiculaire à celle de convergence, principalement par des mécanismes de constriction horizontale. De plus, nous mettons en évidence une dualité rhéologique entre un noyau cratonique stable et sa couverture autochtone lors de processus tardifs de réactivation tectonique.

Geologically-constrained inversion of geophysical data is a powerful method for predicting geology beneath cover. The process seeks 3D physical property models that are consistent with the geology and explain measured geophysical responses. The recovered models can guide mineral explorers to prospective host rocks, structures, alteration and mineralisation. This thesis provides a comprehensive analysis of how the University of British Columbia Geophysical Inversion Facility (UBC–GIF) gravity and magnetic inversions can be applied to subsurface mapping and exploration by demonstrating the necessary approach, data types, and typical results. The non-uniqueness of inversion demands that geological information be included. Commonly available geological data, including structural and physical property measurements, mapping, drilling, and 3D interpretations, can be translated into appropriate inversion constraints using tools developed herein. Surface information provides the greatest improvement in the reliability of recovered models; drilling information enhances resolution at depth. The process used to prepare inversions is as important as the geological constraints themselves. Use of a systematic workflow, as developed in this study, minimises any introduced ambiguity. Key steps include defining the problem, preparing the data, setting inversion parameters and developing geological constraints. Once reliable physical property models are recovered they must be interpreted in a geological context. Where alteration and mineralisation occupy significant volumes, the mineralogy associated with the physical properties can be identified; otherwise a lithological classification of the properties can be applied. This approach is used to develop predictive 3D lithological maps from geologically-constrained gravity and magnetic inversions at several scales in the Agnew-Wiluna greenstone belt in Australia’s Yilgarn Craton. These maps indicate a spatial correlation between thick mafic-ultramafic rock packages and gold deposit locations, suggesting a shared structural control. The maps also identify structural geometries and relationships consistent with the published regional tectonic framework. Geophysical inversion provides a framework into which geological and geophysical data sets can be integrated to produce a holistic prediction of the subsurface. The best possible result is one that cannot be dismissed as inconsistent with some piece of geological knowledge. Such a model can only be recovered by including all available geological knowledge using a consistent workflow process.

Important geochemical and tectonic events in the Paleoproterozoic Era lay the foundation for the status and operation of the modern Earth, including the initial rise of atmospheric oxygen paving the path for animal evolution, and the emergence of modern plate tectonic processes leading to the amalgamation of the Canadian Shield (Laurentia). Rudimentary geological and geochronological documentation of Paleoproterozoic sedimentary basins is the foundation from which we can ask larger questions about geochemical changes or plate tectonic events on the evolving Earth, since those questions are largely answered by analyzing the sedimentary record. This thesis outlines the stratigraphy, detrital zircon U-Pb geochronology, elemental and isotopic geochemistry, and basin evolution of the Paleoproterozoic Penrhyn and Piling basins on the Rae craton in Arctic Canada, which record important tectonic and geochemical events on both a regional and global scale. The concentration of the redox-sensitive trace element, U, in seawater has not been constant throughout geologic time and is linked to changes in oceanic and atmospheric oxygen content. Secular variations in the record of U contents of shales and iron formations indicate that the redox state of the atmosphere-ocean system after the Great Oxidation Event (GOE) was more dynamic than previously thought. Trends towards lower oxygen content recorded after ~2.05 Ga in the middle Proterozoic suggest that oxygen level decreased. This is contrary to traditional models assuming unidirectional atmospheric oxygen rise throughout the Proterozoic. The data demonstrate the earliest signal of oxidative U cycling, manifested in 2.47 - 2.43 Ga iron formations, and show that oxygenation was a protracted process initiated shortly after the end of the Archean. It has been proposed that a global and long-lived magmatic and tectonic shutdown event from ~2.45 to 2.22 Ga played a causal role in the GOE, since it overlaps the time interval in which atmospheric oxygen initially rose on Earth. Coupled U-Pb, Hf, and O isotope data on magmatic and detrital zircon determine that plate tectonic processes continued to operate during this interval. It is argued instead that plate tectonic processes are necessary to promote conditions favorable for atmospheric oxygen to rise.

The Comet Gold Mine is in the Murchison mineral field which lies within the Yilgarn Craton of Western Australia. Several different geophysical methods were used in this study to define the geophysical signatures of sedimentary iron formations (SIF) and altered basalt associated with gold mineralisation. The geophysical surveys carried out at the Comet Gold Mine were gravity, sub-audio magnetics (SAM), transient electromagnetics (TEM) and downhole geophysical logging. Data from previous geophysical surveying were also used, and these included highresolution aeromagnetics and TEMPEST airborne electromagnetics. Other exploration information, such as geology and drillhole data, were integrated with geophysical results to study the geophysical responses and generate a geophysical interpretation map. / The main aim of this study was to generate an understanding of the various geophysical responses of geology and gold mineralisation in the Comet Mine area for future gold exploration in this region. Particularly, the study focused on the ability of the SAM method to map out geology and geophysical response for gold mineralisation. The response from SAM surveying has been investigated over an area of 13 sq kms. The SAM surveying was completed using a transmitter current of 5-8 Amp with a 50% duty cycle at 4 Hz frequency, which was considered the best setting for the Comet area. The SAM anomalies were compared to results from other geophysical methods. The results of all geophysical surveying suggested that the TEM method was also effective for identifying altered sulphide and magnetic altered rock associated with gold mineralisation. / Experiments were carried out using SAM surveying with electrodes in standard surface pits and pits placed directly into the gold mineralised structure. Both surveys showed very similar results, so in this area, surface electrode pits work well for current injection during SAM surveys. The similarities are probably due to the lack of conductive regolith cover in the Comet Mine area. / The SAM response was studied for survey grids using different electrode positions and directions. Experiments in changing SAM electrode position over the same area were carried out along and across geological strike to detect the different geological structure directions. The EQMMR response was different for electrodes oriented at 90º when surveys were repeated over the same area. SAM mainly measures conductive features running sub-parallel to the electrode direction, but the EQMMIP response was mostly the same, despite the difference in electrode direction. In addition, the EQMMIP result was very similar for rotated grids, with some distortion occurring around the main EQMMR anomaly near the Venus open cut pit. Therefore, SAM chargeability was not strongly polarised along the electrode direction like the EQMMR response. This is consistent with the theory of MIP that the method detects the effect of induced polarisation in the earth by virtue of the magnetic fields associated with current flow in polarisable bodies within the earth. / Gravity data were collected along in 4 transects 500 m apart and at 50 m station spacing. 3D gravity modelling using polygonal shapes was completed to a good fit with felsic and mafic rocks by having rock units dip to the SE. Euler depth solution calculations were applied to locate contacts and deep gravity sources. Gravity surveying has also proved to be a useful survey method for geological mapping and locating regional structures. / Ground TEM survey data were used at the Venus prospect to map out conductive zones at depths ranging from 30 to 90 m. All anomaly bodies were interpreted to have a SE dip. The modelled ground TEM results were compared to TEMPEST airborne electromagnetic conductivity depth slices. Both EM survey results showed reasonably similar patterns, but the ground TEM method provided more reliable conductor locations and depth estimations that correlated well with the drilling information and downhole conductivity logging. / Geophysical logs of natural gamma and inductive conductivity were surveyed in 5 drillholes that intersected gold alteration zones. The alteration zones associated with gold mineralised sediments, sulphide and magnetic minerals were identified in the downhole logs as increased conductivity, with a sight increase in the natural gamma response. Natural gamma was usually high above a background of host rock in the gold mineralised shear zones. This was likely due to K associated with the clay rich SIF units, and sericite and biotite from gold related alteration. During this study, drillhole CTRC028 was drilled into a modelled TEM anomaly, and gold mineralised SIF was intersected at the predicted location from the model. / Geophysical survey information (magnetics, gravity, SAM and TEM) and anomalies in the Comet area were found to be primarily controlled by the local structures and mineralisation along these structures. Modelled ground TEM results were compared to TEMPEST airborne, EM data and showed reasonably similar patterns. The geophysical survey data also highlights black shale units, which can produce a false target commonly running parallel to the sulphide altered fault zones and SIF units, because of graphite and sulphide in the black shale. / The TEMPEST data were a valuable guide to bedrock conductivity over the outline project area at Comet, and the follow–up ground TEM and SAM survey data was very useful for accurately pin-pointing anomalies for drill testing. / Geophysical and geological data analysed in this study was used to generate a geophysical interpretation map at 1:5,000 scale. The new interpretation of geological units and structures at Comet will provide geologists with a better understand about the geological and structural setting for mineralisation in the Comet area. For example, the Comet Fault represents a faulted limb of the Comet fold structure that has both limbs dipping to the SE, and plunges to the NE. Magnetic anomalies associated with SIF are considered to correlate with some gold bearing horizons and the location of the Comet Fault, that has become more siliceous and altered by sulphide minerals and magnetite minerals. / It is recommended that other prospect areas in the region should be surveyed using the SAM method in order to identify shallow gold bearing structures and improve geological interpretations ahead of drilling.

[Truncated abstract] The Laverton Greenstone Belt (LGB), located in the northeastern part of the Eastern Goldfields Province (EGP) of the Yilgarn Craton, Western Australia, has a total contained gold endowment of over 690t. An important feature of the gold deposits in the LGB is their close spatial association with granitoids, with many gold deposits located adjacent to, or hosted by, granitoids. Recently-proposed genetic models for Archaean orogenic gold deposits have emphasised the role of granitoids in the formation of ore-deposits, but differ significantly in the nature of that role. Some models suggest that the granitoids are a source of ore-fluids and solutes, whereas others suggest that granitoids exert an important structural control on gold mineralisation. Such competing genetic models for gold mineralisation variably propose either a proximal-magmatic or distal-metamorphic, or less commonly distal-magmatic, source for goldbearing fluids, or mixing of fluids from multiple sources. Isotope geochemistry and geochronological studies are used to constrain the source and timing of auriferous fluids at nine gold deposits in the LGB in an attempt to differentiate between conflicting genetic models. To overcome the lack of detailed deposit-scale geological constraints inherent to any regional study, hypotheses generated from regional datasets are tested in a detailed case-study of the Wallaby gold deposit. The Pb-isotope compositions of ore-related sulphides from deposits in the LGB plot along the line representing crustal-Pb in the Norseman-Wiluna Belt of the EGP, with individual deposits clustering with other nearby deposits based on their geographic location. This trend is similar to that recorded in the Kalgoorlie-Norseman region in the southern EGP, and is consistent with a basement Pb reservoir for gold-bearing fluids. As such, data are consistent with a similar fluid source for all gold deposits. The Nd and Sr isotopic composition of goldrelated scheelite in the LGB clusters very tightly. The inferred ore-fluid composition has a slightly positive εNd, similar to ore fluids at other gold deposits in the EGP for which a proximal magmatic source is highly improbable. As such, Sr and Nd data are consistent with a similar fluid source for the gold deposits analysed in the LGB, but cannot unequivocally define that source. The median S, C and O isotopic compositions of ore minerals from all nine different gold deposits studied in the LGB fall in a very narrow range

Submitted by Simone Souza (simonecgsouza@hotmail.com) on 2017-11-06T14:09:28Z No. of bitstreams: 1 DISS_2014_Flávia Regina Pereira Santos.pdf: 8722372 bytes, checksum: c183f45aa009ebffa0e290e3e4ab1d3a (MD5) / Approved for entry into archive by Jordan (jordanbiblio@gmail.com) on 2018-02-02T14:48:57Z (GMT) No. of bitstreams: 1 DISS_2014_Flávia Regina Pereira Santos.pdf: 8722372 bytes, checksum: c183f45aa009ebffa0e290e3e4ab1d3a (MD5) / Made available in DSpace on 2018-02-02T14:48:57Z (GMT). No. of bitstreams: 1 DISS_2014_Flávia Regina Pereira Santos.pdf: 8722372 bytes, checksum: c183f45aa009ebffa0e290e3e4ab1d3a (MD5) Previous issue date: 2014-03-17 / CAPES / A Província Rondoniana-San Ignácio, na porção sudoeste do Cráton Amazônico, é marcada por um complexo amalgama de terrenos de diferentes idades e origens. O embasamento do Terreno Jauru é constituído por rochas metavulcano-sedimentares e intrusivas ácidas, básicas e ultrabásicas. As rochas metavulcano-sedimentares vem sendo comumente designadas de Grupo Alto Jauru. Mapeamento geológico, petrografia, análise estrutural e geocronologia realizados na região da Fazenda Retiro, a norte da cidade de Araputanga, SW do estado de Mato Grosso, revelam que este Grupo é constituído por biotita-muscovita-quartzo xistos; clorita-biotita-muscovita xistos; granada-cordierita-biotita xisto e estaurolita-andalusita-biotita xisto; associados à granada-sillimanita-biotita gnaisse, biotita gnaisse, anfibolitos e muscovita granito. A petrografia e as relações estruturais indicam que estas rochas foram afetadas por dois eventos deformacionais, Dn e Dn+1, com as foliações associadas Sn (xistosidade e bandamento gnáissico) e Sn+1 (clivagem de crenulação); e três eventos metamórficos: o primeiro evento metamórfico (M1), contemporâneo à Sn de fácies xisto verde inferior; o segundo (M2) associado a fase Sn+1 de fácies xisto verde a anfibolito; e o terceiro evento térmico (M3) de fácies hornblenda-hornfels. A idade de cristalização do biotita gnaisse obtida pelo método U/Pb (SHRIMP) em zircão é de de 1819 ± 6,7 Ma. A interpretação desses dados permite considerar que as rochas do Grupo Alto Jauru são parte de um prisma acrescionário formado no Estateriano. / The Rondoniana-San Ignácio Province, southwestern portion of the Amazonian Craton, is marked by a complex amalgam of terrains from different ages and sources. The basement of one Jauru Terrain consists of metavolcano-sedimentary rocks and intrusive acidic, basic and ultrabasic. The metavolcano-sedimentary rocks has been commonly called Alto Jauru Group. Geologic mapping, petrography, geochronology and structural analysis performed on Retiro Farm region, north of the Araputanga city, SW of Mato Grosso state, reveal that this Group consists of biotite-muscovite-quartz schists, chlorite-biotite-muscovite schists, garnet-cordierite-biotite schist and staurolite-andalusite-biotite schist, garnet-sillimanite associated with biotite-gneiss, biotite gneiss, amphibolite and muscovite granite. The petrography and structural relationships indicate that these rocks were affected by two deformational events Dn and Dn+1, Sn associated with the foliation (schistosity and gneissic banding) and Sn+1 (crenulation cleavage), and three metamorphic events: first metamorphic event (M1), the contemporary Sn lower greenschist facies, the second (M2) associated with Sn+1 phase greenschist to amphibolite facies, and the third thermal event (M3) hornblende hornfels facies. The crystallization age of the biotite gneiss obtained by the method U/Pb (SHRIMP) zircon is 1819 ± 6.7 Ma. The interpretation of these data suggest that the rocks of the Alto Jauru Group are part of a accretionary prism formed in Statherian.

Submitted by Aline de Cassia Carlin null (alinecarlin@yahoo.com.br) on 2016-11-23T10:59:57Z No. of bitstreams: 1 Mestrado_AlineCarlin.pdf: 8299590 bytes, checksum: 2fccc8ef8565c36ad917cbdc0c96c8e3 (MD5) / Approved for entry into archive by Felipe Augusto Arakaki (arakaki@reitoria.unesp.br) on 2016-11-25T17:30:28Z (GMT) No. of bitstreams: 1 carlin_ac_me_rcla.pdf: 8299590 bytes, checksum: 2fccc8ef8565c36ad917cbdc0c96c8e3 (MD5) / Made available in DSpace on 2016-11-25T17:30:28Z (GMT). No. of bitstreams: 1 carlin_ac_me_rcla.pdf: 8299590 bytes, checksum: 2fccc8ef8565c36ad917cbdc0c96c8e3 (MD5) Previous issue date: 2016-10-10 / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / O depósito de ouro Lavra Velha, que pertence ao Alvo de Prospecção Lavra Velha, da empresa Yamana Gold, localiza-se na cidade de Ibitiara, centro-oeste do Estado da Bahia e borda oeste do domínio fisiográfico da Chapada Diamantina, situado no Aulacógeno do Paramirim, na região norte do Cráton São Francisco. O depósito foi recentemente inserido na classe de modelo IOCG (Iron Oxide Cooper Gold), onde a mineralização de ouro se hospeda em brechas hematíticas sericitizadas. O principal objetivo do trabalho foi caracterizar química e petrograficamente as rochas encaixantes do depósito Lavra Velha, cujas litologias predominantes são metatonalitos e meta-quartzo diorito. Estas rochas encontram-se completamente alteradas, com atuação dos processos hidrotermais predominando sobre a deformação de baixo strain, resultando em intensa sericitização e formação de óxidos de ferro, além de cloritização, epidotização, carbonatação e, localmente, albitização. A análise petrográfica, suportada pela análise química, sugere que as rochas encaixantes são correspondentes alteradas do Granitoide Ibitiara, metamorfizadas, deformadas e alteradas hidrotermalmente. O Granitoide Ibitiara e o Granito Matinos apresentam comportamento de magmatismo misto e afinidade para ambiente de arco magmático (sin-colisional) ou orogênico, com idades correlatas ao ciclo orogênico Transamazônico. A intrusão do Granitoide Ibitiara ocorre, provavelmente, em ambiente mais raso da crosta, sugerindo que fluidos hidrotermais e mineralizantes sejam mais tardios. Apesar de integrado até o momento à classe de depósitos IOCG, a análise tectono-estrutural e hidrotermal do depósito Lavra Velha sugere que a mineralização de ouro tenha origem relacionada à fase mais tardia de evolução da bacia do Espinhaço, relacionada à inversão do aulacógeno do Paramirim. / The Lavra Velha gold deposit, which belongs to the prospecting target “Lavra Velha” of the Yamana Gold Company, is located in Ibitiara, Bahia’s central west and the western edge of the physiographic domain of the Chapada Diamantina, situated in Paramirim aulaconge, in northern of São Francisco Craton. The deposit was recently insert into the IOCG model class (Iron Oxide Cooper Gold), where the gold mineralization is hosted at hematite sericitic breccias. The main objective of the study was the chemical and petrographic characterization of the host rocks of the Lavra Velha deposit, whose predominant lithologies are meta-tonalites and metaquartz diorite. These rocks are completely altered due to hydrothermal process, that predominates under the deformation at low-strain rate, resulting in intense sericitization and iron oxide formation, also chloritization, epidotization, carbonatation and, locally, albitization. The petrographic analysis, supported by chemical analysis, suggests that the host rocks correspond to metamorphosed, deformed and hydrothermalized portion of Ibitiara Granitoid. The Ibitiara Granitoid and Matinos Granite show behaviors of mixed magmatism and also affinity for arc magmatic (syn-collisional) or orogenic ambient with correlative age to the Transamazônico Cycle. The Ibitiara Granitoid intrusion probably occurs at a shallower crust environment, suggesting that the hydrothermal and mineralizer fluids are later. In spite of the Lavra Velha deposit has being classified as IOCG’s class, the tectonic, structural and hydrothermal analysis suggests that the gold mineralization has originated during Espinhaço basin later deformation stage, related to inversion of the Paramirim aulacogen.

Made available in DSpace on 2015-04-22T21:58:29Z (GMT). No. of bitstreams: 1 Dissertacao_Joelson Soares.pdf: 6826963 bytes, checksum: 26430a23509522e7bc61cc5e2c669c45 (MD5) Previous issue date: 2008-05-06 / FAPEAM - Fundação de Amparo à Pesquisa do Estado do Amazonas / The Neoproterozoic is marked by major climatic changes that interfere with the Crucially in biological evolution and paleoceanográfica of our planet, and mainly characterized by periods of low overall glacial that achieved latitudes. This dramatic period in the history of the planet is recorded in layers carbonate termed carbonate layers that overlap directly diamictic glaciers. In this work one Neoproterozoic cap carbonate 20 m thick was Tangara described in Limestone mine, Tangara da Serra, Mato Grosso. That sequence comprises the Mirassol d West formations (dolomite) and Guide (limestone) belonging to the lower group macaws. The cover is composed of dolomitic dolograinstones peloidais pink with inverse grading, a parallel lamination and truncation of low angle, in addition to discontinuous layers of fibrous crystals calcite (gypsum pseudomorphs second?), interpreted as records of a shallow to moderately deep platform with hypersalinity events. The cover Limestone consists of rolled and massive, siltstone rich in iron oxide, and lime thin with wavy bedding megamarcas interpreted as deposits moderately deep mixed platform dominated by waves. Limestone with fine corrugated laminating / ripple marks and fans crystals (pseudomorphs second aragonite), intercalated with shales were interpreted as deposits deep platform and supersaturated in CaCO3. With calcareous structures Slip including convoluted laminations and syn-sedimentary faults characterized slope deposits, while Neptunian dykes, filled with limestone breccias, and deformed layers between non deformed layers suggest seismic activity. Three stratigraphic surfaces divide the carbonate succession studied: S1 separates the covers dolomitica and limestone and is interpreted as transgressive surface, while surfaces S2 and S3 within the limestone cover are considered limits facies. Facies deformed occur throughout the sequence, separated by intervals without strain, and were split into three packages (A, B and C). Packages A and C exhibit ductile-brittle structures like folds, faults and bedding convoluted, while the B package contains structures formed in brittle regime as failures and fractures. Analysis of C and O isotopes showed negative values ​​similar to found in other carbonate covers the world. The data 13C isotope values ​​between -4 and -6 in the case dolomite , limestone while in the case 13C the values ​​reaches to -7 without co- variance of the 18 O isotope indicates change by meteoric fluids or by dolomitization . The sequence described in Tangara Sierra expands the occurrence of carbonate layers in South America and corroborates the interpretation of an extensive carbonate platform post- glaciation Puga , related to Marinoano event , this part of the Amazon Craton. / O Neoproterozóico é marcado por importantes mudanças climáticas que interferiram da forma crucial na evolução biológica e paleoceanográfica do nosso planeta, sendo caracterizado principalmente por períodos de glaciação global que alcançaram baixas latitudes. Este período dramático da história do planeta está registrado em camadas carbonáticas denominadas de capas carbonáticas que sobrepõem diretamente diamictitos glaciais. Neste trabalho uma capa carbonática neoproterozóica de 20 m de espessura foi descrita na mina Calcário Tangará, região de Tangará da Serra, Mato Grosso. Essa seqüência compreende as formações Mirassol d Oeste (dolomítica) e Guia (calcária) que pertencem à parte inferior do Grupo Araras. A capa dolomítica é composta por dolograinstones peloidais rosados com gradação inversa, laminação plano-paralela e truncamentos de baixo ângulo, alem de camadas descontínuas de cristais fibrosos de calcita (pseudomorfos segundo gipsita?), interpretados como registros de uma plataforma rasa a moderadamente profunda com eventos de hipersalinidade. A capa calcária consiste em siltitos laminados e maciços, ricos em óxido de ferro e calcários finos com acamamento de megamarcas onduladas, interpretados como depósitos de plataforma mista moderadamente profunda dominada por ondas. Calcários finos com laminação ondulada/marcas onduladas e leques de cristais (pseudomorfos segundo aragonita), intercalados com folhelhos, foram interpretados como depósitos de plataforma profunda e supersaturada em CaCO3. Calcários com estruturas de escorregamento incluindo laminações convolutas e falhas sin-sedimentares caracterizam depósitos de talude, enquanto diques neptunianos, preenchidos por brechas calcárias, e camadas deformadas entre camadas não deformadas sugerem atividade sísmica. Três superfícies estratigráficas dividem a sucessão carbonática estudada: S1 separa as capas dolomitica e calcária e é interpretada como superfície transgressiva, enquanto as superfícies S2 e S3, dentro da capa calcária são consideradas limites de fácies. Fácies deformadas ocorrem ao longo de toda a sucessão, separadas por intervalos sem deformação, e foram subdivididas em três pacotes (A, B e C). Os pacotes A e C apresentam estruturas dúctil-rúptil como dobras, falhas e acamamento convoluto, enquanto o pacote B contém estruturas formadas em regime rúptil como falhas e fraturas. A análise de isótopos de C e O mostrou valores negativos semelhantes aos encontrados em outras capas carbonáticas pelo mundo. Os dados de isótopos de 13C apresentam valores entre -4 e -6 na capa dolomítica, enquanto que na capa calcária os valores de 13C alcançam até -7 sem co-variância dos isótopos de 18O, indica alteração por fluidos meteóricos ou pela dolomitização. A sucessão descrita em Tangará da Serra amplia a ocorrência de capas carbonáticas na América do Sul e corrobora com a interpretação de uma extensa plataforma carbonática pós-glaciação Puga, correlata ao evento Marinoano, nesta parte do Cráton Amazônico.