O significado da idade do magmatismo, reconhecimento das séries magmáticas e ambientes tectônicos que controlaram a origem das rochas metavulcânicas do Greenstone Belt da Vila Nova (GBVN), é uma importante ferramenta para entender a evolução do Escudo das Guianas durante o Paleoproterozóico. Este trabalho apresenta novos dados geoquímicos de rochas metavulcânicas e de U/Pb em zircão (LA-MC-ICPMS), que foram suplementados por petrografia, dados estratigráficos e estruturais obtidos através de mapeamento geológico e descrição de furos de sondagem. Na região de Vila Nova, as unidades do GBVN repousam sobre o embasamento Arqueano composto por ortognaisses, metagranitos e anfibolitos do Complexo Tumucumaque. A base do GBVN é composta por metabasaltos e metabasaltos andesíticos, sotoposto por um domínio superior metassedimentar com rochas químico exalativas e metavulcânicas subordinadas. As rochas metavulcânicas incluem anfibolitos e anfibólio xistos, cujos corpos estão alongados segundo a xistosidade regional de direção NW-SE. A geocronologia pelo método U-Pb em zircão mostra uma idade de 2.154 ± 6 Ma para um meta-andesito da porção inferior do GBVN. O evento de metamorfismo orogênico esteve associado a três eventos deformacionais. Os eventos D1 e D2 formaram a xistosidade (S1), preservada como dobras intrafoliais (F2) e a clivagem de crenulação (S2), originadas a partir de movimentos de cavalgamento. O pico metamórfico (M1) está marcado pela assembleia plagioclásio+hornblenda+granada e, plagioclásio+hornblenda+diopsídio, indicando temperaturas entre 450 e 650 °C e pressão entre 4 e 6 kbares. Os metabasitos compreendem Fe-toleítos e Mg-toleítos com afinidade komatitica, composições geoquímicas enriquecidas em LILE e ETR e empobrecidas em HFSE (com anomalias negativas de Nb, Ti e P) e padrões de ETR semelhantes ao MORB. As características observadas indicam um magmatismo toleítico relacionado à bacias de retro-arco e arco de ilhas de 2.15 Ga no Escudo das Guianas. / The significance of the age of magmatism, magma series and tectonic settings that controls the origin of metavolcanic rocks of Vila Nova Greenstone Belt (VNGB) is an important issue in order to understand the evolution of Guiana Shield in Paleoproterozoic times. This work presents new U-Pb LA-ICP-MS geochronological and geochemical analyzes carried out on zircon grains and metavolcanic rocks of the Vila Nova greenstone belt (VNGB) which were supplemented by petrography, and stratigraphic and structural data acquired through description of boreholes and field work. In the Vila Nova region, the VNGB units rest on the Archaean basement composed of orthogneisses of the Tumucumaque Complex. The lower portion of the VNGB is composed of metabasalts and andesitic metabasalts, supported by an upper metasedimentary domain with exhalative chemical rocks and subordinate metavolcanic rocks. The metavolcanic rocks include amphibolites and amphibole schists, whose bodies are elongated according to the regional NW-SE schistosity. U-Pb zircon geochronology data showed an age of 2154 ±6 Ma for a meta-andesite of the lower portion of VNGB. Orogenic metamorphism event followed by three deformation events were recognized. The D1 and D2 events formed the schistosity (S1), preserved as intrafolial folds (F2) and the crenulation cleavage (S2), derived from thrust movements. The assemblages plagioclase + hornblende + garnet and plagioclase + hornblende + diopside define the metamorphic peak (M1-M2) with temperatures from 450-650 °C and lithostatic pressure between 4 and 6 kbars. The metabasites comprise Fe-tholeiites and Mg-tholeiites with komatiitic affinity, geochemical compositions enriched in LILE and REE and depleted in HFSE (with negative Nb, Ti and P anomalies) and MORB-like REE patterns. The observed features indicate an expressive magmatism related to back-arc basins and island arcs at 2.15 Ga in Guiana Shield.

The Bird River sill (BRS) is composed of layered mafic-ultramafic intrusive bodies which intruded the Bird River greenstone belt in southeastern Manitoba. Layered intrusions, such as those that collectively make-up the BRS, are important hosts to base and precious metal deposits. This study was initiated to examine and develop an emplacement model for the western half of the BRS and to establish the controls on Cr-Ni-Cu-PGE mineralization. The BRS intrusions were emplaced through multiple-magmatic injections into different stratigraphic levels in the Lamprey Falls Formation. It is interpreted that the central BRS intrusions are connected and represent a single conduit system. The BRS and the Lamprey Falls Formation are overlain by the metasedimentary rocks of the Peterson Creek Formation and are overturned. The stratigraphy of the BRS is divided into four series which are from the base upwards: 1) marginal mafic series, 2) ultramafic series, 3) transition series, and 4) mafic series. All significant concentrations of Cr-Ni-Cu-PGE are contained in the ultramafic series. Mineralization is magmatic in origin with significant Ni-Cu and PGE remobilization associated with late felsic magmatism. Ni-Cu remobilization is also associated with mineralized shear zones that cross-cut the BRS and Lamprey Falls Formation. The sulphur source could not be determined unambiguously based on sulphur isotopes alone but the δ34S values of the BRS intrusions suggests that the sulphur in the BRS is magmatic in origin and that two of the BRS bodies may have assimilated external sulphur. The findings of this investigation have considerable economic implications. The model that each BRS body is an individual intrusion implies each body may contain its own style of mineralization. Secondly, the Page body of the BRS is interpreted to represent a turbulent magmatic environment and to be the first intrusion to form at the lowest stratigraphic level. The magmas that formed the stratigraphically higher BRS intrusions are believed to have passed through the Page intrusion. Therefore, the Page body is an excellent exploration target as it represents a turbulent environment in which significant amounts of primitive magma have passed through which are two key factors in the formation of Ni-Cu-PGE deposits.

The Bird River sill (BRS) is composed of layered mafic-ultramafic intrusive bodies which intruded the Bird River greenstone belt in southeastern Manitoba. Layered intrusions, such as those that collectively make-up the BRS, are important hosts to base and precious metal deposits. This study was initiated to examine and develop an emplacement model for the western half of the BRS and to establish the controls on Cr-Ni-Cu-PGE mineralization. The BRS intrusions were emplaced through multiple-magmatic injections into different stratigraphic levels in the Lamprey Falls Formation. It is interpreted that the central BRS intrusions are connected and represent a single conduit system. The BRS and the Lamprey Falls Formation are overlain by the metasedimentary rocks of the Peterson Creek Formation and are overturned. The stratigraphy of the BRS is divided into four series which are from the base upwards: 1) marginal mafic series, 2) ultramafic series, 3) transition series, and 4) mafic series. All significant concentrations of Cr-Ni-Cu-PGE are contained in the ultramafic series. Mineralization is magmatic in origin with significant Ni-Cu and PGE remobilization associated with late felsic magmatism. Ni-Cu remobilization is also associated with mineralized shear zones that cross-cut the BRS and Lamprey Falls Formation. The sulphur source could not be determined unambiguously based on sulphur isotopes alone but the δ34S values of the BRS intrusions suggests that the sulphur in the BRS is magmatic in origin and that two of the BRS bodies may have assimilated external sulphur. The findings of this investigation have considerable economic implications. The model that each BRS body is an individual intrusion implies each body may contain its own style of mineralization. Secondly, the Page body of the BRS is interpreted to represent a turbulent magmatic environment and to be the first intrusion to form at the lowest stratigraphic level. The magmas that formed the stratigraphically higher BRS intrusions are believed to have passed through the Page intrusion. Therefore, the Page body is an excellent exploration target as it represents a turbulent environment in which significant amounts of primitive magma have passed through which are two key factors in the formation of Ni-Cu-PGE deposits.

The Bernic Lake Formation in the Bird River greenstone belt consists dominantly of mafic to felsic arc volcanic and volcaniclastic rocks, with varying amounts of mafic to felsic intrusive rocks, including the Bernic Lake pegmatite group. U-Pb geochronoligical analyses on selected samples around the Bernic Lake area, indicate that the Tanco gabbro, the Birse Lake granodiorite and the volcanic rocks of the Bernic Lake Formation are contemporaneous ca. 2724 Ma and form part of a singular volcanic and subvolcanic complex. The highly evolved, LCT-type, rare element-bearing Bernic Lake pegmatite group, including the world class Tanco pegmatite, was emplaced in the Bernic Lake Formation during a belt-scale tectonomagmatic event associated with G3 deformation between ca. 2650 and 2640 Ma. Early and rarely preserved isoclinal folding in the Bernic Lake Formation attributed to G1 deformation was followed north-south directed compression resulting in refolding and transposition of G1 structures by east-west trending upright F2 folds. Continued compression caused strain localization and south-side-up shearing along the North Bernic Lake Shear Zone (NBLSZ), which juxtaposes MORB-like basalt of the south panel to the south against arc rocks of the Bernic Lake Formation to the north. G3 deformation is characterized by a spaced S3 fracture cleavage that overprints the penetrative S2 fabric, and dextral reactivation of the NBLSZ. Pegmatitic melt ascended from depth along the reactivated NBLSZ during this time and was emplaced both within the shear zone and within rock units adjacent to it. The shapes and orientations of the pegmatites are controlled in part by the rheology of the host rocks into which they were emplaced. Rheologically competent lithologies responded to G3 strain by brittle fracture and the pegmatites occurring therein are flat and tabular; rheologically incompetent lithologies responded to G3 strain by ductile-brittle deformation and the pegmatites therein are irregular, folded, and/or boudinaged. The contrasting styles suggest that the pegmatites intruded while the rocks of the Bernic Lake Formation were at or near the brittle-ductile transition.

The Bernic Lake Formation in the Bird River greenstone belt consists dominantly of mafic to felsic arc volcanic and volcaniclastic rocks, with varying amounts of mafic to felsic intrusive rocks, including the Bernic Lake pegmatite group. U-Pb geochronoligical analyses on selected samples around the Bernic Lake area, indicate that the Tanco gabbro, the Birse Lake granodiorite and the volcanic rocks of the Bernic Lake Formation are contemporaneous ca. 2724 Ma and form part of a singular volcanic and subvolcanic complex. The highly evolved, LCT-type, rare element-bearing Bernic Lake pegmatite group, including the world class Tanco pegmatite, was emplaced in the Bernic Lake Formation during a belt-scale tectonomagmatic event associated with G3 deformation between ca. 2650 and 2640 Ma. Early and rarely preserved isoclinal folding in the Bernic Lake Formation attributed to G1 deformation was followed north-south directed compression resulting in refolding and transposition of G1 structures by east-west trending upright F2 folds. Continued compression caused strain localization and south-side-up shearing along the North Bernic Lake Shear Zone (NBLSZ), which juxtaposes MORB-like basalt of the south panel to the south against arc rocks of the Bernic Lake Formation to the north. G3 deformation is characterized by a spaced S3 fracture cleavage that overprints the penetrative S2 fabric, and dextral reactivation of the NBLSZ. Pegmatitic melt ascended from depth along the reactivated NBLSZ during this time and was emplaced both within the shear zone and within rock units adjacent to it. The shapes and orientations of the pegmatites are controlled in part by the rheology of the host rocks into which they were emplaced. Rheologically competent lithologies responded to G3 strain by brittle fracture and the pegmatites occurring therein are flat and tabular; rheologically incompetent lithologies responded to G3 strain by ductile-brittle deformation and the pegmatites therein are irregular, folded, and/or boudinaged. The contrasting styles suggest that the pegmatites intruded while the rocks of the Bernic Lake Formation were at or near the brittle-ductile transition.

Thesis (MSc (Geography and Environmental Studies))--University of Stellenbosch, 2005. / 81 Leaves printed on single pages i-xi, preliminary pages and numbered pages 1- 70. Includes bibliography, list of tables and list of figures. / Digitized at 300 dpi color PDF format (OCR), using KODAK i 1220 PLUS scanner. / ENGLISH ABSTRACT: Geological field mapping is often limited by logistical and cost constraints as well as the scope and extent of observations possible using ground-based mapping. Remote sensing offers, among others, the advantages of an increased spectral range for observations and a regional perspective of areas under observation. This study aimed to determine the accuracy of a collection of image classification techniques when applied to ASTER reflectance data. Band rationing, the Crosta Technique, Constrained Energy Minimization, Spectral Correlation Mapping and the Maximum Likelihood Classifier were evaluated for their efficiency in detecting and discriminating between greenstone and granitoid material. The study area was the Archaean Barberton Greenstone Belt in the eastern Mpumalanga Province, South Africa. ASTER reflectance imagery was acquired and pre-processed. Training and reference data was extracted from the image through visual inspection and expert knowledge. The training data was used in conjunction with USGS mineral spectra to train the five classification algorithms using the ERDAS's software package. This resulted in abundance images for the target materials specified by the training data. The Maximum Likelihood Classifier produced a classified thematic map. The reference data was used to perform a rigorous classification accuracy assessment procedure. All abundance images were thresholded to varying levels, obtaining accuracy statistics at every level. In so doing, threshold levels could be defined for every abundance image in such a way that the reliability of the classification was optimized. For each abundance image, as well as for the output map of the Maximum Likelihood Classifier, user's- and producer's accuracies as well as kappa statistics were derived and used as comparative measures of efficiency between the five techniques. This information was also used to assess the spectral separability of the target materials. The Maximum Likelihood Classifier outperformed the other techniques significantly, achieving an overall classification accuracy of 81.1% and an overall kappa value of 0.748. Greenstone rocks were accurately discriminated from granitoid rocks with accuracies between 72.9% and 98.5%, while granitoid rocks showed very poor ability to be accurately distinguished from each other. The main recommendations from this study are that thermal infrared and gamma-ray data be considered, together with better vegetation masking and an investigation into object orientated techniques. / AFRIKAANSE OPSOMMING: Geologiese veldkartering word algemeen beperk deur logistiese en koste-verwante faktore, sowel as die beperkte bestek waartoe waarnemings met veld-gebasseerde tegnieke gemaak kan word. Afstandswaarneming bied, onder andere, 'n vergrote spekrale omvang vir waarnemings en 'n regionale perspektief van die area wat bestudeer word. Hierdie studie was gemik daarop om die akkuraatheid van 'n versameling beeld-klassifikasie tegnieke, toegepas op ASTER data, te bepaal. Bandverhoudings, die Crosta Tegniek, "Constrained Energy Minimization", Spektrale Korrellasie Kartering, en Maksimum Waarskynlikheid Klassifikasie is evalueer op grond van hul vermoë om groensteen en granitoied-rotse op te spoor en tussen hulle te onderskei. Die studiegebied was die Argalese Barberton Groensteengordel in die oostelike Mpumalanga Provinsie in Suid Afrika. 'n ASTER refleksie beeld is verkry, waarop voorverwerking uitgevoer is. Opleidings- en verwysingsdata is van die beeld verkry deur visuele inspeksie en vakkundige kennis. Die opleidingsdata is saam met VSGO mineraalspektra gebruik om die vyf klassifikasie algoritmes met behulp van die ERDAS sagteware pakket op te lei. Die resultaat was volopheidsbeelde vir die teikenmateriale gespesifiseer in die opleidingsdata. Die Maksimum Waarskynlikheid algoritme het 'n geklassifiseerde tematiese beeld gelewer. Met behulp van die verwysingsdata is 'n streng akkuraatheidstoetsing prosedure uitgevoer. Vir alle volopheidsbeelde is 'n reeks drempelwaardes gestel, en by elke drempelwaarde is akkuraatheidsstatistieke afgelei. Op hierdie manier kon 'n drempelwaarde vir elke volopheidsbeeld vasgestel word sodat die drempelwaarde die betroubaarheid van die klassifikasie optimeer. Vir elke volopheidsbeeld, asook vir die tematiese kaart verkry van die Maksimum Waarskynlikheid klassifikasie, is gebruikers- en produsent-akkuraathede en kappa statistieke bereken. Hierdie waardes is gebruik as vergelykende maatstawwe van akkuraatheid tussen die vyf tegnieke, asook van die spektrale skeibaarheid van die onderskeie teikenmateriale. Die Maksimum Waarskynlikheid klassifikasie het die beste resultate gelewer, met 'n algehele klassifikasie akkuraatheid van 81.1%, en 'n gemiddelde kappa waarde van 0.748. Groensteenrotse kon met hoë akkuraathede van tussen 72.9% en 98.5% van granitoiedrotse onderskei word, terwyl granitoiedrotse 'n swak vermoë getoon het om van mekaar onderskei te word. Die belangrikste aanbevelings vanuit hierdie studie is dat termiese uitstralingdata asook gamma-straal data geimplimenteer word. Beter verwydering van plantegroei en 'n studie na die lewensvatbaarheid van objekgeorienteerde metodes word ook aanbeveel.

O significado da idade do magmatismo, reconhecimento das séries magmáticas e ambientes tectônicos que controlaram a origem das rochas metavulcânicas do Greenstone Belt da Vila Nova (GBVN), é uma importante ferramenta para entender a evolução do Escudo das Guianas durante o Paleoproterozóico. Este trabalho apresenta novos dados geoquímicos de rochas metavulcânicas e de U/Pb em zircão (LA-MC-ICPMS), que foram suplementados por petrografia, dados estratigráficos e estruturais obtidos através de mapeamento geológico e descrição de furos de sondagem. Na região de Vila Nova, as unidades do GBVN repousam sobre o embasamento Arqueano composto por ortognaisses, metagranitos e anfibolitos do Complexo Tumucumaque. A base do GBVN é composta por metabasaltos e metabasaltos andesíticos, sotoposto por um domínio superior metassedimentar com rochas químico exalativas e metavulcânicas subordinadas. As rochas metavulcânicas incluem anfibolitos e anfibólio xistos, cujos corpos estão alongados segundo a xistosidade regional de direção NW-SE. A geocronologia pelo método U-Pb em zircão mostra uma idade de 2.154 ± 6 Ma para um meta-andesito da porção inferior do GBVN. O evento de metamorfismo orogênico esteve associado a três eventos deformacionais. Os eventos D1 e D2 formaram a xistosidade (S1), preservada como dobras intrafoliais (F2) e a clivagem de crenulação (S2), originadas a partir de movimentos de cavalgamento. O pico metamórfico (M1) está marcado pela assembleia plagioclásio+hornblenda+granada e, plagioclásio+hornblenda+diopsídio, indicando temperaturas entre 450 e 650 °C e pressão entre 4 e 6 kbares. Os metabasitos compreendem Fe-toleítos e Mg-toleítos com afinidade komatitica, composições geoquímicas enriquecidas em LILE e ETR e empobrecidas em HFSE (com anomalias negativas de Nb, Ti e P) e padrões de ETR semelhantes ao MORB. As características observadas indicam um magmatismo toleítico relacionado à bacias de retro-arco e arco de ilhas de 2.15 Ga no Escudo das Guianas. / The significance of the age of magmatism, magma series and tectonic settings that controls the origin of metavolcanic rocks of Vila Nova Greenstone Belt (VNGB) is an important issue in order to understand the evolution of Guiana Shield in Paleoproterozoic times. This work presents new U-Pb LA-ICP-MS geochronological and geochemical analyzes carried out on zircon grains and metavolcanic rocks of the Vila Nova greenstone belt (VNGB) which were supplemented by petrography, and stratigraphic and structural data acquired through description of boreholes and field work. In the Vila Nova region, the VNGB units rest on the Archaean basement composed of orthogneisses of the Tumucumaque Complex. The lower portion of the VNGB is composed of metabasalts and andesitic metabasalts, supported by an upper metasedimentary domain with exhalative chemical rocks and subordinate metavolcanic rocks. The metavolcanic rocks include amphibolites and amphibole schists, whose bodies are elongated according to the regional NW-SE schistosity. U-Pb zircon geochronology data showed an age of 2154 ±6 Ma for a meta-andesite of the lower portion of VNGB. Orogenic metamorphism event followed by three deformation events were recognized. The D1 and D2 events formed the schistosity (S1), preserved as intrafolial folds (F2) and the crenulation cleavage (S2), derived from thrust movements. The assemblages plagioclase + hornblende + garnet and plagioclase + hornblende + diopside define the metamorphic peak (M1-M2) with temperatures from 450-650 °C and lithostatic pressure between 4 and 6 kbars. The metabasites comprise Fe-tholeiites and Mg-tholeiites with komatiitic affinity, geochemical compositions enriched in LILE and REE and depleted in HFSE (with negative Nb, Ti and P anomalies) and MORB-like REE patterns. The observed features indicate an expressive magmatism related to back-arc basins and island arcs at 2.15 Ga in Guiana Shield.

Submitted by Everaldo Pereira (pereira.evera@gmail.com) on 2017-02-20T01:26:33Z No. of bitstreams: 1 Dissertaçao_zilda_Pena.pdf: 20071531 bytes, checksum: 636c5527dec3a4e97a3755ec06ed6311 (MD5) / Made available in DSpace on 2017-02-20T01:26:33Z (GMT). No. of bitstreams: 1 Dissertaçao_zilda_Pena.pdf: 20071531 bytes, checksum: 636c5527dec3a4e97a3755ec06ed6311 (MD5) / Esta dissertação apresenta novos dados petrográficos e litogeoquímicos para as rochas da sequência vulcanossedimentar do Greenstone Belt do Rio Itapicuru (GBRI), na região da Mina Fazenda Brasileiro. O trabalho baseou-se principalmente em estudos nas rochas de subsuperfície da mina Fazenda Brasileiro (MFB) especificamente na sequência Fazenda Brasileiro. O Cráton do São Francisco (CSF), onde está localizada a área de estudo, é o maior remanescente de terrenos Precambrianos preservados na Plataforma Brasileira. Os terrenos do GBRI estão situados na porção nordeste do CSF, na área conhecida como Núcleo Serrinha (NSer). Possui aproximadamente 80x40 km, sendo rodeado por um embasamento granítico-gnáissico e cortado por vários granitos de idade Arqueana. Como a maior parte dos greenstones do CSF, o GBRI foi afetado por metamorfismo de fácies xisto-verde a anfibolito de baixo grau durante o Paleoproterozóico, aproximadamente a 2,07-2,08 Ga, um período em que a região em estudo também sofreu muitas intrusões de granitos potássicos pós-tectônicos e metamorfismo regional de alta temperatura. Os estudos petrográficos revelaram a presença de diversas texturas, tanto ígneas reliquiares, como texturas que indicam a atuação do metamorfismo (crenulação, lepidoblástica, nematoblástica, granoblástica) e que marcam a foliação descrita pela rocha. A partir dos estudos petrográficos foram identificadas: (i) rochas máficas-ultramáficas, essencialmente basaltos, (ii) e uma sequencia de lavas félsicas e intermediárias variando em composição de andesitos a riolitos. Ambas são cortadas por TTGs Arqueanos e Paleoproterozóicos, caracterizada na área de estudo pelos granitos Araci, Barrocas e Teofilândia, e também pelo magmatismo alcalino potássico como, por exemplo, o corpo de Barroquinhas. Ocorrem ainda corpos intrusivos sub-vulcânicos, representados por riodacitos, quartzo-dioritos. (iii) A sequência metassedimentar consiste basicamente de metapelitos, metatufos e xistos grafitosos, associados a carbonatos, e muitas vezes mineralizados em sulfetos e metais-base, que representam um menor componente. Devido às evidentes dificuldades na delimitação das litologias nas unidades e sequências clássicas da literatura preferiu-se estabelecer critérios litogeoquímicos para a descrição das amostras estudadas. As análises químicas mostraram a presença de dois conjuntos distintos: (i) toleiitico e (ii) cálcio-alcalino. Foi ainda possível identificar rochas com características sugestivas de um vulcanismo mais alcalino (shoshonítico) e distinguir rochas em campo descritas como sedimentares, como em verdade rochas vulcânicas muito finas (cinzas, aglomerados) e alteradas. Os dados aqui apresentados colaboram trazendo uma melhor compreensão das variações temporais e de caráter químico entre os diversos termos litológicos da MGB. O fato é que as rochas descritas como “Sequência Fazenda Brasileiro” estão relacionadas a eventos geológicos bem distintos, envolvendo diferentes pulsos de vulcanismo intercalados por sedimentação. As dificuldades na descrição das rochas do GBRI, na individualização dos pulsos vulcânicos, associada à confusão de nomenclatura entre os termos de mina e os clássicos levam à proposição de inúmeros modelos evolutivos para a região, o que torna ainda mais complexo o seu entendimento. Esta complexidade relaciona-se a fatores que incluem: (i) a extensa evolução química de cada uma das series magmáticas identificadas, com a presença de termos ultrabásicos a ácidos tanto na série toleiítica quanto na cálcio alcalina; (ii) a dificuldade de se obter uma idade mais precisa para os diferentes grupos de rochas em função da limitação das fases datáveis, (iii) a pronunciada recristalização e o intenso fluxo de fluidos ligados ao processo de hidrotermalismo, metamorfismo e deformação, que mascaram e agravam a complexidade estrutural da área.

Submitted by Everaldo Pereira (pereira.evera@gmail.com) on 2017-06-28T20:40:03Z No. of bitstreams: 1 Joilma Santos - Dissertação.pdf: 6021802 bytes, checksum: 02f3bb9f14736f8b87203b40546477c4 (MD5) / Made available in DSpace on 2017-06-28T20:40:03Z (GMT). No. of bitstreams: 1 Joilma Santos - Dissertação.pdf: 6021802 bytes, checksum: 02f3bb9f14736f8b87203b40546477c4 (MD5) / Na Plataforma Sul-Americana, inúmeros greenstone belts arqueanos (~ 2,9 a 3,2Ga) são identificados no Cráton do São Francisco, Estado da Bahia, entre eles destacam-se os de Riacho de Santana, Umburanas, Contendas Mirante e Mundo Novo. O greenstone belt de Riacho de Santana (GBRS) localizado na porção sudoeste do Estado da Bahia, Brasil, ocorre como unidade no embasamento cristalino do Bloco Guanambi-Correntina. Segundo Silveira & Garrido (2000), o GBRS apresenta três unidades litoestratigráficas reconhecidas: (i) Unidade Inferior, compreende rochas ultramáficas komatiíticas com finas intercalações de meta-basaltos e meta-gabros, associados a formações ferríferas bandadas (BIFs), quartzitos, meta-cherts, rochas cálcio-silicáticas e xistos aluminosos; (ii) Unidade Intermediária, constituída por meta-basaltos e meta-gabros, meta-tufos de composição intermediária a ácida, xistos aluminosos e xistos grafitosos, e (iii) Unidade Superior, compreende uma sequência de rochas silicáticas-carbonáticas. Neste trabalho são apresentados as descrições geológicas, petrográficas, as análises de química mineral e de geoquímicas de elementos maiores, traços e terras raras das rochas meta-vulcânicas máficas da Unidade Intermediária com inferências sobre os processos responsáveis pela formação destas rochas. As rochas meta-vulcânicas máficas da Unidade Intermediária do GBRS são caracterizadas por apresentarem texturas granoblástica e nematoblástica, tendo como minerais predominantes a actinolita/tremolita, hornblenda e plagioclásio e, subordinadamente assinala-se a presença de minerais opacos e titanita. Ocorre como minerais secundários o quartzo, epídoto e carbonatos. Sinais de alterações secundárias estão registradas nos cristais de plagioclásio, através dos processos de saussuritização e sericitização. Apesar das rochas não apresentarem mais a mineralogia primária preservada, foi identificado resquícios das texturas ígneas ofítica e intergranular. Em todas as amostras, a parâgenese mineral metamórfica observada é característica da fácies xisto verde (actinolita + hornblenda + andesina - média de 37,35% An). A química mineral permitiu classificar os anfibólios no grupo dos cálcicos, e dentro deste grupo como Fe-hornblenda, com razões Mg/(Mg + Fe+2) entre 0,39 e 0,46. Os cristais de plagioclásio apresentam composição de andesina, com teores de anortita em torno de 40,93–33,09%. Os dados de temperatura adquiridos pela análise dos plagioclásios sugerem que o magma atingiu no mínimo, temperaturas da ordem de 1128oC a 1187oC. As rochas meta-vulcânicas máficas foram classificadas como basaltos, demonstrando baixa razão de álcalis versus sílica, demonstrando caráter toleítico, fortemente enriquecido em ferro. Com a evolução magmática observa-se empobrecimento de Cr, Ni, CaO e Al2O3 e enriquecimento de SiO2, TiO2, FeOt, K2O, Na2O e elementos incompatíveis. O comportamento geoquímico dos elementos maiores sugere um forte controle dos minerais plagioclásio e clinopiroxênio no fracionamento magmático. Padrões de elementos terras raras (ETR) normalizados para o manto primitivo sugerem que o magma primário das rochas meta-vulcânicas máficas do GBRS foi derivado a partir de reservatórios mantélicos primitivos ou por uma mistura entre reservatórios enriquecidos e empobrecidos. Os padrões planos de ETR/pesados indicam processo de fusão relativamente rasa com ausência de granada na fonte. Algumas amostras apresentaram enriquecimento anômalo de elementos LIL e presença de anomalia negativa de Sr, similar àquelas observadas do embasamento, sugerindo que o processo de contaminação destes magmas com as rochas do embasamento granítico-gnáissico do Bloco Guanambi-Correntina teve um papel importante na formação dessas rochas. / ABSTRACT - In the South American Plataform, many Archean greenstone belts (~ 2.9 to 3.2Ga) are identified in São Francisco Craton, Bahia State, among them stand out from the Riacho de Santana, Umburanas, Contendas Mirante and Mundo Novo. The Riacho Santana greenstone belt (RSGB) located in southwestern Bahia, Brazil, occurs as a unit in the basement of Guanambi-Correntina Block. According to Silveira & Garrido (2000) presents the RSGB recognized three lithostratigraphic units: (i) Lower Unit comprises ultramafic komatiites with thin intercalations of meta-basalts and meta-gabbro, associated with the banded iron formations (BIFs), quartzites, meta-cherts, calcisilicate rocks and aluminous schists; (ii) Intermediate Unit, consisting of meta-basalts and meta-gabbro, meta-tuffs of intermediate to acid composition, aluminous schists and graphitic schists, and (iii) Higher Unit comprises a sequence of carbonate-silicate rocks. In this work, the descriptions will be presented geological, petrographic, the analysis of mineral chemistry and geochemistry of major, trace and rare earth elements of meta-volcanic mafic rocks of the Intermediate Units with inferences about the processes responsible for the formation of these rocks. The meta-volcanic mafic rocks of the Intermediate Unit are characterized by presenting inequigranular, nematoblastic and granoblastic textures, with the predominant mineral tremolite/actinolite, hornblende and plagioclase and subordinate occurs the presence of opaque minerals and titanite. The secondary minerals include quartz, epidote and carbonates. Secondary changes are recorded in plagioclase crystals, through the processes of saussuritization and sericitization. Although the rocks have no more preserved primary mineralogy was identified remnants of igneous ophitic and intergranular textures. In all samples, the metamorphic mineral paragenesis observed is characteristic of greenschist facies (actinolite + hornblende + andesine - average of 37.35% An). The mineral chemistry allowed to classify the group of calcic amphiboles, and within this group as Fe-hornblende, with ratios of Mg/(Mg + Fe+2) between 0.39 and 0.46. The plagioclase crystals have the composition of andesine, with anorthite content of around 40.93 to 33.09%. The temperature data of plagioclase suggest that the magma reached a minimum temperature in the range of the 1128oC 1187oC. The meta-volcanic mafic rocks were classified as basalts, showing a low ratio of alkali versus silica, showing tholeiitic character, strongly enriched in iron. With the magmatic evolution is observed depletion of Cr, Ni, CaO and Al2O3 and enrichment of SiO2, TiO2, FeOt, K2O, Na2O and incompatible elements. The geochemical behavior of major elements suggests a strong control of the minerals plagioclase and clinopyroxene at magmatic fractionation. Patterns of rare earth elements (REE) normalized to the primitive mantle suggest that the primary magma of the rocks of the mafic meta-volcanic from the RSGB was derived from primitive mantle reservoirs or a mixture of enriched and depleted reservoirs. Standards plans heavy REE indicate relatively shallow melting process with the absence of garnet in the source. Some samples showed anomalous enrichment of LIL elements and presence of negative anomalies of Sr, similar to those observed basement, suggesting that the process of contamination of these magmas with granitic-gneissic rocks of Guanambi-Correntina basement had an important role in the formation of these rocks.

Submitted by Everaldo Pereira (pereira.evera@gmail.com) on 2017-12-12T14:01:06Z No. of bitstreams: 1 Dissertação Daniel.pdf: 7519004 bytes, checksum: 974f5d52c5c0cb196fbd59d1da9636c5 (MD5) / Approved for entry into archive by NUBIA OLIVEIRA (nubia.marilia@ufba.br) on 2017-12-12T16:11:13Z (GMT) No. of bitstreams: 1 Dissertação Daniel.pdf: 7519004 bytes, checksum: 974f5d52c5c0cb196fbd59d1da9636c5 (MD5) / Made available in DSpace on 2017-12-12T16:11:13Z (GMT). No. of bitstreams: 1 Dissertação Daniel.pdf: 7519004 bytes, checksum: 974f5d52c5c0cb196fbd59d1da9636c5 (MD5) / Os depósitos de ouro da Faixa Mansinha estão confinados em uma zona de cisalhamento sinistral rúptil-dúctil que está localizada em metadacitos, metatufos líticos, metatufos de cristal e rochas da Unidade Metassedimentar metamorfisadas na facies xisto verde e com trend preferencial Norte Sul com mergulho médio de 60º para oeste localizado no setor centro norte do Greenstone belt do Rio Itapicuru, NE Bahia. Alterações de carbonatação e sericitização são pervasivas nas rochas sedimentares e vulcânicas de caráter félsico dentro da zona de cisalhamento. Dois depósitos foram estudados, sendo: o M11, com corpo mineralizado caracterizado por um veio tabular de quartzo fumê com espessura de até 2 metros e comprimento de 500 metros, relacionado à metatufos de cristal e metassedimentos de origem turbiditica, com orientação subparalela à foliação da encaixante; e o M3, em que o minério está associado a 4 gerações de veios tabulares de quartzo leitoso e a um sistema de stockwork na parte norte do depósito, ambos encaixados nos metatufos de cristal associados. O ouro ocorre na forma de grãos livres finamente disseminados ou relacionados com sulfetos nos veios de quartzo. Estudos de inclusões fluidas por microtermometria revelaram que os veios de quartzo são amplamente dominados por inclusões primárias, pseudosecundárias de CO2± (CH4+N2) classificadas como inclusões do Tipo I, e inclusões H2O-CO2-(± CH4 ± N2) de baixa salinidade (<3% eq. NaCl) classificadas como do Tipo II. O valor de ThCO2 indicou uma variação da densidade de CO2 de 0,6 para 0,93 g/cm3 para inclusões do tipo I, e variação de 0,75-0,82 g/cm3 para as inclusões do tipo II. A variação mais ampla da densidade de CO2 das inclusões carbônicas pode ter resultado de um aprisionamento do fluido do veio dentro de um regime de pressão variado, ou de seu reequilíbrio durante a deformação continua dentro do domínio da zona de cisalhamento e redução da pressão durante o soerguimento. Os dados obtidos relacionados ao comportamento estrutural, alterações hidrotermais e de inclusões fluidas, combinados com dados de outros depósitos (C1, Antas I, II e III, todos da Unidade Maria Preta), possibilitam a classificação desses depósitos como de ouro do tipo lode orogenético. / ABSTRACT - The gold deposits of the Mansinha Strip are confined in a sinistral brittle-ductile shear zone that is located in metadacites, lithic metatuffs, crystal metatuffs and rocks of Metassedimentary Units, which are metamorphosed in a greenschist facies and with preferential North South trend with average dip of 60º to the west located in the north-central sector of the Greenstone belt of Itapicuru River, NE Bahia. Alteration is pervasive throughout the shear zones and characterized by carbonatization and sericitization of sedimentary and felsic volcanic rocks. Two deposits were studied: M11 with a mineralized body characterized by a tabular smoky quartz vein with a thickness of up to 2 meters and a length of 500 meters, related to crystal metatuffs and metasediments of turbiditic origin, with a subparallel orientation to the foliation of the host rock; And the M3 in which the ore is associated with 4 generations of milky quartz tabular veins and a stockwork system in the northern part of the deposit, both embedded in the associated crystal metatuffs. Gold appears as free finely disseminated grains or sulfide-related in the quartz veins. Fluid inclusions studies by microthermometry revealed that quartz veins are largely dominated by primary, pseudo-secondary inclusions of CO2 ± (CH4 + N2) classified as Type I inclusions, and H2O-CO2 inclusions (± CH4 ± N2) of low salinity (<3% eq NaCl) classified as Type II. The ThCO2 data indicated a variation in the CO2 density of 0.6 to 0.93 g/cm3 for Type I inclusions, and variation from 0.75-0.82 g/cm3 for Type II inclusions. The broader variation of the CO2 density for the CO2-rich fluid could have been the result of trapping of the vein fluid under a variable pressure regime, or by its re-equilibration during continuous deformation within the shear zone domains and reduction of the overburden pressure during uplift. The data obtained related to structural behavior, hydrothermal alterations and fluid inclusions, combined with data from other deposits (C1, Antas I, II and III, all of the Maria Preta Unit), make it possible to classify these deposits as lode gold orogenetic.